I use BRS12N 4U and I feel comfortable... but slightly weak smashes... I want to buy JS9 4U.. and need more info ~ i think JS9 is 76 holes, so it help me stringing easy (I'm stringing my self).
I think that you would better off with a 3U or something head heavier like a thruster, if you think your smash is weak. Regardless 72 or 76 makes no difference in stringing. For the 76 holes you need some scrap string. Only 80 holes are a bit pain in the ass.
Why not try putting on some lead tape on your BS12N and see if that helps? Victor make lead tape stripes which they call poweriser tape. Inexpensive and might just be what you need.