Power, not much more than a well built 2.8, torque, about 20-30 ft lbs more. However, more important is it will be spread over a much wider band. I don't know if you have already checked out the sites about the strokers. If you have, then you have an idea of what you are getting into. It is a fair amount more $$ for the increase in power/torque. A turbo yields more power per $$. But it is more complicated.
Check out The Datsun Workshop, if you haven't already.
Sorry, head choice. It really doesn't matter. The N 42 is an easy choice. The P-90A is good with a slight shave to up the Compression ratio and the 1mm HKS head gasket. You are looking at mid 9's for the CR. I use it, but for different reasons. And you need to make sure the hydraulic adjusters are good. You cannot buy new ones anymore.
Thanks for the input. I have already checked out all of the sites with stroker info, but I wanted to hear from someone else who has one. I'll probably go with the N42 head which is currently on the motor in my daily driver 2+2. I just wanted a liitle more power out of the limo Z and figured a stroker woul be the easier way to go. I'm planning on buying a 2 seater to build into a turbocharged track and weekend car. I talked to a member of my local Z club who has built an awesome stroker 280Z, injected with larger injectors, high compression(11:1) bored throttle body, balenced and blueprinted valve train, ported and polished N42 head, a big nasty cam, headers, exhaust, and a SDS stand alone computer with DIS ignition. He's dynoed 230 at the wheel and his car HAULS!