The 12Y-49 with the S-P supercharger was fitted to the D.520 Amélioré - a modified D.520 with some changes that were learned from the D.524 (These changes were planned to be made for all D.520-based platforms until the armistice stopped it from happening). The tests were later (1941), but it does give a pretty good indication as to how 520's fitted with the -49 would perform.
In the table I linked below, you can see that it was quite a significant boost to the base D.520 with the -45. It's just barely slower than the Bf 109 E-4/N at 570 kph / 354 mph compared to the E-4/N's 580 kph / 360 mph. That speed difference isn't huge, and becomes almost trivial when you remember that the D.520 was regularly able to outmanoeuvre the 109.
Rather than the Emils, the Friedrichs are the biggest concerns since those are much better performing and first show up in October. The D.525 and VG.35 with the -51 would be closer, but the F-1 is still a good bit ahead of both.