As I recall (may not be correct), the EX250 puts about 25~26hp to the ground vs. the B4's 40(?).
That's a 65% increase in power for only a 17% increase in weight...
ex250 = 355/26 = 13.5 lbs/HP
gsf400 = 418/40 = 10.5 lbs/HP
Based on my experience with both, I think the 250 is more nimble. I'd have to ride them back to back to be 100% on that though. The 250 certainly has a shorter wheelbase by over 2", which is Huge.