I agree with what was said about the level of horsepower you are at.

If everything is laid out and the Dynomax can outflow the Flowmaster, is it worth it to cut your exhaust off (is it falling apart, does it need to be replaced?) and change everything out just to gain maybe 5 hp at WOT?

A little bit of back-pressure is a good thing for everyday part-throttle driving. If it's balls to the wall WOT performance you are after, maybe a set of electric cut-outs would be the way to go instead.

Off-topic, but I have a single Flowmaster on my 360 Magnum and that thing has at least 130,000+ miles on it and the case is still solid with no sign of leaks anywhere. Very happy with the build quality.