Mandoble,
Doing virtually the same test off-line, but with the fuel use set to 0 so as to maintain constant fuel weight, the Spit9 made 340/333 (wep/no wep) at 5k and 360/355 at 10k.  I haven't done any FWs yet, but results for Spit9, La7, G-10, P-51D, and N1K2 will be up soon.  Granted that most planes approach their top speeds very slowly so it is possible that no observable movement took place for a 30 sec period.  My top speeds were taken after 5 minutes level flight and, in the case of the P-51, a little later because it still had observable increase in speed.  Exact conditions were:
Fuel as close to 25 minutes duration as possible (P-51: 50%, La-7: 100%, G-10: 100%, N1K2-J: 50%, Spit9: 75%)
Fuel Use set to 0 (well, 0.001)
Combat Trim On
Auto Level On
Speed dropped to 150 TAS then accelerated with and without WEP (I'll have accel numbers posted, too)
Max speed taken after 5 minutes.  Not sure how these will look in post, but here are numbers from Excel:
   1k   5k   10k   15k   20k   25k   30k                     
G-10   362/331   387/356   400/375   418/383   440/406   430/415   418/403
La-7   387/369   400/381   400/400   395/395   406/406   398/398   362/362
N1K2-J   340/331   350/344   351/349   356/350   369/362   350/349   331/325
P-51D   370/351   378/374   400/394   400/399   415/402   428/425   422/412
Spit9   321/318   340/333   361/355   380/375   380/378   401/395   399/399
HaMmeR 
Originally posted by MANDOBLE:
Well, Wulfe, it seems you are not available to do some TA test. No problem, I did them for you:
The test:
190A8 4x20, 190F8 2x20, 190A5 4x20, SpitIX 2x20 + 2x50.
All 75% fuel + DT.
Tests were done climbing to the test alt (no wep), droping the DT and full power and then WEP ON until 30 secs with no speed neddle movements.
5k:
190A5 -> 330 mph
190A8 -> 325 mph
190F8 -> 325 mph
SpitIX -> 320 mph
10k:
190A5 -> 305 mph
190A8 -> 305 mph
190F8 -> 302 mph
SpitIX -> 318 mph
higher that 10k = more advantage for the spit.
190A/F have a minimal edge only up to 5k (more or less). So, the conclusion is that 190A5 (the fastest at 5k) is a faster plane than SpitIX... ...LOL, better luck with next absurd assumption mate.
Hey, and, at least for me, there are more than a single plane of motion. SpitIX is faster than any 190A/F at any alt in the vertical.