B20 bottom end, CAms, or ATS Final drive 4.9????

[dualstage]

hi everyone i was wondering which of these i should do first..... if i just buy a b20b bottom end what kind of gains would i be expecting, i know i would have to put higher compression pistons, resleeve and other stuff, but just a stock b20 block for now slapped with my gsr head? Or should i just get skunk2 stage 2 cams or something equivalent, or should i get the ATS final drive gear which is 4.9 for quicker acceleration, im gonna get all of these in the future but which would give me maximum gains first