The P-51D and K were placarded as having a Vfe of 405 KIAS for the first notch...
Now, as to the turn performance, I can't comment on that. The acceleration seems about right to me BTW, as does the climb of the P-51D in AH (but then, I'm never flying with less than full fuel, I suspect many of the claims of 4000fpm sustained climbs come from reduced fuel load...)
blk (AT)