I tested 3 cards on Street Fighter 4:
5450 - a slight improvement over the onboard graphics - Character movements still pretty slow in fighting sequences with all graphic options on.
6450 - an improvment over the 5450 - About 50% faster in fighting sequences, but still slower than it should be with all graphic options on
r7 250 - A big improvement - all fighting sequences were 100% full speed even with all graphics enabled.
Now granted, those tests were with the basic pc, not the modder (maybe the modder will run that 6450 better than the basic did). Once I went through the testing on those cards when I bought modder pc's, I just went with the r7 250, and that's why I have told anyone who has asked to go with the r7 250, it's a better value than the 7750, and ran everything 100% so far that I have tried with no lagging.
My buddy's basic pc, I initially installed a 6450 for him, then told him to come over and try out the r7 250 when I got it in... his reaction was "Oh man, yeah... now this is what I'm talking about, now it's running perfectly."
This has been a public service message from Mr. Passive Aggressive.