I haven't personally driven a RB26 powered S15, but as I said a mate owned a RB26 180sx and he said it was stupidly overpowered and quite heavy in the frontend. The S15 may be a bit better but I doubt it. If you are doing it for a drift car, then you have the perfect combination, if you want a good handling road / track car (unless you were obviously going to cut the firewall and move the engine back) I would personally keep the SR20. If you build a motor properly, you can still push big numbers and have reliability.From what I hear the handling is not upset that much considering the weight of the RB26. A stroker kit on an SR20 is a cool mod but if spending that kind of money you are looking for more power obviously. So if yer a Nissan head wouldnt you run an RB26 to push big bhp & have some reliability.
Personally Id rather have a JZ engine but then again thats me.
the JZ engine is pretty much bulletbroof. Awesome engine, but as I said it depends on what you want.