I just purchased a new BW PSAII. It is 51@28 and I draw 28. I have 2 other recurves that are 50 lbs. the widow just seems a little heavier. The other 2 do not have FF strings and the widow does. Would the string make it feel heavier.

No.  Widows feel heavier because they have a lot of preload and build weight early in the draw.  

They are fast, but there's no free lunch.

Just as Jeff said, they have a lot of the weight built early in the draw. It also may be heavier than marked, I have owned 10-12 Widows and a couple were 2-3#s heavier than marked. Shawn