My exhaust system is very sad right now. It has some of that flexpipe on the passenger side and its cracked and falling appart. I know where Im taking it here in Sacramento, a good place I think. I have flowmasters on here right now but im thinking they may be a little tired, how do I know? I think there the 40 series also. I need something for now, I have a 350, and something that will be good to go when I drop in a BBC. I think maybe the 50 series? w/ 2.5 pipe?

I doubt if you've "worn out" Flowmasters as there is really nothing to wear out. They are probably already 2.5" in and out as that's what most shops carry and they use adapters to go smaller. If the inlet/outlets haven't been butchered, you should be able to reuse them. If you want a little more quiet, go with the 50's.