gyrene, I found an official chart on 109 flap speeds, and in fact 109s can (and did) safely use up to 20 degrees flaps at speeds up to 450 kph! (which is 280 mph!!)
so 217 isnt even close either!
That being said, if 20 degrees is allowable at 280, 10-15 should be fine at 300+ agreed?
google "109 flap deployment speed" and you can find it in the top 3 results in ww2aircraft. net
Not to mention it's well known that Marseilles used flaps all the time at high speed to gain extra lead for deflection shooting!
Honestly though, if this improved historical flap deployment ability makes the 109 more competitive with top allied rides, (which it most certainly will) do you really think it will be fixed?