m54 also does not require shimming of the valves which is costly even if you do it yourself and a pain in the ass. I would go M54 from a ZHP model if possible over the s54 but that's just for practicality.
ZHP's had the problematic Alpina(IIRC) cams didn't they? And anyway, they M54B30 had about 230hp. Hoveringuy^ on r3v easliy surpassed that number with tuning. An E30 with a tweaked M54B30 would be quicker than an E46 M3.
