It's far too hard to generalise, but by porting the head, you will lose peak torque, so unless you have a turbo that can blow hard enough, the engine will lose it's punchy feel.

Depends on how you drive it.

I made 290lb/ft on a standard head at 250bhp, it was a gearbox breaker. Once the head was ported, peak torque dropped to 250lb/ft, but it felt stronger through the rev-range. If you don't have at least a stage 3 turbo, don't bother IMO.