"Marcel had the opportunity to fly the American P-51 and the P-47. In comparing these allied aircraft with the Yak, he clearly said that the Yak was a superior aircraft. When Marcel flew for the RAF flying the Spitfire, he was not impressed with the English aircraft at all. "
http://aviationartstore.com/albert_2.htm
I think that if Yak used Merlin engie from Great Britain like P51-D it would be the best fighter. P51 mustang was upgraded it's frame and used Merlin engine to get impressive speed. If Yak was upgraded it's frame and used powerful Merlin egnine no other fighter would touch it. Because it's more agile than P51-D.

yak with different engine