Stumbled on this thread when looking for a few things related to some off-topic tangents in recent discussions including the Fw 187 among other designs. And, political issues aside, there's a few technical points that no one seemed to touch on in this discussion, or at least manage to gloss over to the point it missed actual discussion.
Look at the cooler intake on V5.
Compare that with the radiator intake on an A-0, the only version to sort of enter some kind of service. These radiators did not have to deal with the heat from the more powerful DB 601.
This is just one of many differences between a prototype aircraft and something which could actually fight. You are completely ignoring this. You don't have to be an aerodynamicist or undertake sophisticated calculations to work out that these kind of differences will degrade the performance figures that you keep quoting.
The image of the V5 nacelles looks very much like a retractable radiator in the fully retracted position. Several of the Fw 187 prototypes (including the V1) used similar arrangements on the Jumo 210. (and somewhat reminiscent of Heinkel retractable radiators)
The A0 preproduction aircraft switched to bulkier fixed chin radiators as also shown in the above pictures. (I'm not sure why the change was made, but I suspect at least partially to save on weight and to simplify the design of those aircraft -it was also done on the prototypes targeting the later 2-seater 'destroyer' modifications that led to the A0)
There may be some other oddities with the V5's cooling system, but that does at least look like a retractable radiator.
Additionally it was the V6 prototype that (at least according to Wiki's sources) employed an evaporative surface cooling system (described in a manner akin to the surface cooled He 100), not the V5. It also used a DB-600 opposed to the 601 apparently employed on the V5.
The V5, from what I can gather from all the resources already pooled into this thread, seems to be the closest to a speculative single-seat 'proper' DB-601 powered aircraft, albeit not operationally equipped. And even if it did use an exotic radiator design there's still one other area that hadn't been even suggested in this thread: adapting low-drag embedded radiators in the wings. (more like the Mosquito, Bf 109, Spitfire, and I believe Bf 110) That's something that was never tested on the aircraft and could have significantly reduced drag. (the retractable radiator arrangement may have worked well too if developed to operational status, and that was, after all, the practical solution the He 100 finally settled on)
the steam seperator in german called Dampfabschneider, was part of the engine, and it's main duty was to hold the water liquid circle of the engine bubble free, so that no steam bubbles could get at the water circle of the engne.
It was also used for normal high pressure water cooling at the DB 605, Jumo 213 and DB 603.
The first german engines as the Jumo 211A-H (Jumo F was the first with high pressure water cooling) and the DB 601A-N (DB 601E as the first with high pressure water cooling)were not high pressure water cooling engines and the part of the glycol was very smal and at the jumo engine only part of the water cycle at winter month. The engine highest temperature of the non high pressure water cooling engine was 90 C, for the high pressure water cooling engines 110-120 C. It was higher at the second generation engines with steam seperator.
This seems to point to the V5 not using the surface cooling of the likes of the He 100 and Fw 187 V6, but an adaptation of the existing open-loop unpressurized water cooling system of the DB 600 to allow for temperatures exceeding the boiling point of water without having steam bubbles appearing in the cooling jacket. Technically this would be a form of evaporative cooling, but only as a side effect (main intent was increased water temperature) so SOME sort of condenser would be needed but only a small one (to return the collected steam to the main water circuit or reservoir). DB made this mechanism obsolete by adopting a pressurized cooling system with the DB 601E, so it's no wonder further development was abandoned. (admittedly, I'd been under the impression the 601A had already introduced this feature)
However, it appears Jumo 211 (and apparently early 601 models) did indeed adopt such a system to allow some improvement in cooling area efficiency over conventional unpressurized systems. (this too became obsolete with the introduction of pressurized cooling on the 211-F and later models)
And on the Fw 187 in general: yes the really useful/exciting potential of the airframe is mostly hypothetical since those variants were never built or at least not configured in a combat ready manner, and the entire high performance single seat twin engine fighter concept was continually at conflict with RLM doctrine and other politics as well. That said, I still think there's a reasonable indication that it could have developed in a similar manner to the P-38, perhaps with fewer problems (no turbo issues, better roll rate, no obvious compressibility issues) and similarly adaptable as a long range fighter, interceptor, and fighter-bomber/attack aircraft. (and possibly limited use as a late-war night fighter once more compact AI radar becomes available, similar to the P-38M)
I also find it odd that the Jumo 211 was never tested on the aircraft and rarely if ever comes up in literature relating to it. It's not as good as the 601, but still a reasonably capable design that should have fit well enough (and far better than the 210).
Edit: additionally, while the 2 (let alone 3) seater configurations were cramped and left little room for further expansion, a single seat version should have been more flexible. This could include moving the cockpit back to make room for more guns in the nose. (and adjust for COG with the added guns making things more nose-heavy -especially for the likes of MK-108; 2x 108s in the nose and 4 151/20s in the cheeks seems realistic)