My initial impression is that BOTH the 109 and the IIa are too slow at sea level, but by roughly the same amount. Personally, I wouldn't want the IIa any faster unless the 109's speed was adjusted upward to its historical value as well. Besides wanting the IIa and 109 to be historically accurate performance-wise for the sake of accuracy, it means from a gameplay aspect both fighters can reach altitude a little quicker, closing speeds on enemy bombers are faster, and headons with opposing fighters that much scarier.
The Ia is too slow, IMHO at this early point, in that it shouldn't be that much slower than the IIa. If the IIa and the Ia are not superior to the 109's, they should at least be a very serious threat. I did shoot down a vulching 109 at Hawkinge while flying a IIa. He certainly knew I was there because he dodged my poorly-aimed tracers as I overshot him. He could've escaped at that point while I was reversing to re-engage (as any smart experten 109 pilot would), but this 109 opted instead to make another strafing run. This gave me the time I needed to come around and line him up -- something that we couldn't do with our nerfed RAF fighters pre-patch. I don't believe the current patched Ia has the performance to effectively counter a boom & zooming 109 strafing its home airfield, but I certainly found the patched IIa does.
I had one sortie today in the 100-octane Rotol, thanks to your air start at Eastchurch. It feels like it has similar performance at sea level to the earlier Rotol (retail 1.15950 version) -- except in the current version you go to 12 lbs overboost to get up to ~270 mph (with noise, vibration, and possible blown engine at 3000 rpms) where before you got the same speed at 6.25 lbs boost, 2500/2600 rpms - no vibration and you could maintain that speed for a whole gas tank. I helped shoot down a Stuka that was attacking Ramsgate; the Hurricane seems to hold steadier than a Spit while firing -- but that might only be my imagination. I then proceeded on to Dover and managed to ram Bliss' dawdling 109 from behind. Actually, he backed up into me -- a new maneuvre for the 109 with this latest patch, I believe. I'd be interested to hear JTDawg's take on the 100-octane Rotol.
Again, take everything above with a grain of salt based on initial trials of aircraft in an online combat environment. I haven't yet taken any of these RAF a/c into a rear area to give 'em a serious going over, with careful checks of instrument readings.