VK45 is a very nice V8, will be lighter than an RB26 and offer a heap of torque without boost
Dunno what would have to be done to fit one, but it would certainly be nice (they came in AWD variants too!).
Alternatively you can stroke a VQ35de which will drop right into your engine bay and there are plenty of options for both N/A or Turbo for them
(as an aside, you can get a 3.8L stroker kit designed to redline at 12000rpm... other parts of the engine will need to be strengthened and lightened of course, but I am sure spinning a 3.8L VQ to 11500 would sound awesome.)
If you want a factory turbo engine to modify, go the VQ25det over the VQ30det or RB.
If you want the extra capacity, simply get aftermarket VQ35de crank and rods that can deal with a heap of boost.
VQ35de would be the easiest way though, they are easy to source, used in a number of models and the yanks have HEAPS of fun bits for them.