ummm, by aftermarket are you talking motor bits? like pistons, etc??? If so, 99 percent of people don’t touch that shit anyways.
Upgrade bits? All bolt ons are the same for the two in terms of selection. The Nissan Skyline is not exactly a rare car to upgrade.
I don’t see how it’s it cheaper to upgrade a SR.
Turbos cost the same, cams cost the same, injectors cost the same, exhausts are the same, IC’s are the same, what’s more $$$ on the RB? Aparts from slightly more costs on injectors, pistons and anything that requires two more of.
It’s also pretty common knowledge that the short stroke combined with iron block make it pretty effin bulletproof. Dude in Quebec runs 10’s on a stock bottom end.