Getting back to the original subject with 1100-1200hp there isn't enough power for carrying fuel, armament and keeping good performance. Look again at the spitfire MK II data. Lets assume that they can stick even an extra 30 IMP gallons inside the plane (getting rid of the pesky fixed tank) and rig a 30-45 imp gallon drop tank. The drop tank takes care of forming up and climbing to altitude ( some of these planes could burn 25-35 gallons just getting to 30,000ft). Now you have used some internal fuel for warming up and take-off but you are at combat altitude with over 100 imp gallons of fuel or 30-40 more than an "interceptor" would have. While 5-6% more weight has a negligible effect on speed it does have a fair effect on climb, ceiling, and ability to turn.
Ability to turn is not simply how tight the turn radius is but how how fast speed bleeds off in the turn and how tight or at what rate the plane can turn and maintain altitude, not have to dive to maintain speed. Some of these early fighters can only maintain speed in a hard (4-6 "G") turn by loosing several thousand feet of altitude per minute.
Good performance includes climb and altitude as well as speed. One source gives a late model Japanese KI 61 (two type Ho-5 cannon and two H-103mg) as needing 7 minutes to climb to 16,400ft while a MK II Spitfire can get to 20,000ft in the same time. The Spitfire has nearly 5,000ft more service ceiling. While nobody fights at or near the service ceiling it means that the operational and combat ceilings are probably in the Spitfires favor by 3-4,000ft.
But in as escort role, you have burned off most of that fuel so the weight difference in minimal.
Weight is not everything, the Mustang was much heavier than the Spit, which was itself heavier than the 109. In fact the Mustang and 190 were very similar in weights. Yet despite all that weight the Mustang could hold its own in turning contests with both.
By that logic the supreme fighter was the 109, followed by the Spit and the 190 and Mustang following up as also runs. The P-47 being completely useless.
There is some bit Post hoc ergo propter hoc arguments going on here. Along the lines if: "well they didn't do it because they couldn't do it with Spits. Only the P-47s and P-51s had the magical qualities necessary for MR, LR and VLR escort roles", all the extra fuel and so on had no affect on them whatsoever".
I've just been reading excellent "The Bombing War' by Richard Overy. he makes the point that the RAF simply did not do "counter force" (a more encompassing description than just escorting). It was not part of their dogma, either night or day. What little they did (and despite the propaganda it was very little), was always after the fact and as a response to terrible losses, really to get the politicians off their back and try and preserve some of morale with the crews, as much as anything else.
So these things were not technical in nature, they were deliberate choices that were made. For the RAF this applies to night fighter support as well, what little they applied was pathetic, as many people (in the RAF itself) said at the time.
Note that the USAAF was also initially dead against escort fighters (or counter force to be more exact) too. In fact Eaker was dead against them full stop. It was Hap Arnold that was the pusher (and had endless fights with Portal, all documented too, very interesting reading).
One of the reasons why Eaker got moved sideways and people like the superb Doolittle were put in (a very unappreciated person, he was the one that created the layered escort and also set them free - within limits of course, the US's Park in my view, a superb air tactician).
Again, as always, Dowding was different. I contend that if he had remained, ideally been CAS, with Park as head of Fighter Command then things would have been very, very different. (at least there would have been no nonsense about Malta and NA, plus there would have been no starving of VLR aircraft for the BoA).
Note Dowding had no issues with improving range whatsoever, in fact it was a priority for him. Correctly reasoning (since he had been responsible for everything that had been done to date, like the Spit, Hurricane, radar, world best C&C and so on) that if you set the requirements then the manufacturers will make it happen and people like Park will create the training and tactics to apply it properly. After all the spec he created for the Spit and Hurricane was science fiction at the time in a RAF ruled by bi-planes.
So, just like today (sadly people never seem to change) a lot of people ended up dying because some prats at the top screws up and have bees in their bonnet about something (like model trains, read RV Jones, my father actually knew him, he was not impressed).
You can pick many (sadly far too many) examples of this in the years since WW2 and right now (think F-35 for example, the Bolton Paul Defiant of its time).
Talking about that pig, Dowding spent huge amounts of time fending off the Air Ministry about that plane. They loved it, wanted heaps of squadrons dedicated to it, he managed to keep the deaths down fortunately.