TF & Speedmaster Flow Tests

Im a rookie with a dumb question but how do these compare with stock x or J heads in terms of flow numbers? how much is t be gained going aftermarket? I understand aluminum is easier to port polish and modify etc. I am in a situation now where I have a set of J's with 2.02s that need to be sent out Im figuring 700 is to rebuild but the set as cores are pobably worth 250 so the math is basically 950 and a set of speedmasters are in that ball park. I am thinking if I get the j s redone and dont use them i couldnt get 950 for them...decisions decisions :) I also have a set of 1.88 360 Js freshly done...need a boottm end for those.