ABSOLUTE BONKERS!!!!!
the mkI is BETTER than the mkIa.... i did this twice cause i didnt believe it the first time...
at 18k WEP boost (4lb) coarse pitch.... i can hit ~260 IAS thats what...340TAS?
at the SAME at SAME boost and pitch... i can only hit 220 ISA in the mkIa
260IAS is still 20mph too slow but its a whopping 40 faster than the 'a' version (which should be the SAME as the mkI in terms of top speed)
Edit: i even think the climb rate is better for the mkI vs mkIa but im not sure