To elaborate on an earlier post, please refer to this for the true speeds of the spitfire IIa. You will see the game speeds are off:
Spitfire IIa speed trials
Height MPH IAS PEC Comp RPM Boost
1,000 290 294 -8.5 -0.2 2990 +8.8
2,000 294 294 -8.5 -0.4 " +8.8
3,000 298 294 -8.5 -0.6 " +8.8
5,000 306 293 -8.5 -1.1 " +8.8
6,500 311 292 -8.5 -1.4 " +8.8
10,000 325 290 -8.5 -2.2 " +8.8
13,000 337 287 -8.5 -3.0 " +8.8
15,000 344 285 -8.5 -3.5 " +8.8
16,500 350 283 -8.5 -4.0 " +8.8
18,000 354 280 -8.5 -4.3 " +8.3
20,000 350 269 -8.5 -4.5 " +6.2
23,000 344 251 -8.4 -4.6 " +3.6
26,000 335 233 -7.8 -4.4 " +1.5
28,000 329 220 -7.2 -4.3 " +0.2
30,000 321 206 -6.3 -4.1 " -0.9
17,550* 354 282 -8.5 -4.3 " +8.8
Here is the link aswell:
http://www.spitfireperformance.com/spitfire-II.html
it also lists other spitfire models speeds