The A8 can run away from Spit16 and Ki84 yak3, something the A5 have to fight against.
The newly perked Spit14 47m and 51b/d forces the A8 to turn and get chewed up by the turn'y planes planes, best bet is to roll in between the trees and hope the fast plane auger or is a bad shot.
The A9 with TS engine was faster with mw50 made 1.82 ATA, and would probably be closer with the faster planes at the deck.
The A5 is faster than the A8. About the only thing the A8 does better in terms of speed is retain the E longer, and why I do not know. So if the speeds begin at 400+ TAS, then the A8 probably can keep ahead of the pursuing lot you mentioned, if the speeds started at 250 TAS then the A8 will get caught. Likewise, the A5 will be able to keep ahead of the lot you mentioned longer if the speeds started slower, but ultimately the A5 is simply faster than the A8.
One of the best dog fights I've ever had while in a A5 has been at 18-22k vs a P51D. It went back and forth for 10+ minutes, neither of us could gain a true advantage. Finally, I took a risk in getting him in a rolling scissors with too little E and he was able to hang with me and got a shot. My error, his gain. He won.
Don't ever discount the A5 in the 190 roster, it is a workhorse and isn't too far behind the Dora in speed, and outside of firepower (30mm option) the A5 is better than the A8 in terms of handling, turn, acceleration, speeds, and stability/forgiveness.