I've done both, and I can say hands down go turbo, turbo is a guaranteed power adder, I've seen and personally experienced big bore kits and while they do add some power, its still nothing like a turbo. with the older age of these pro's there's good deals to be found for some used kits out there, or buy new.
Even if you ran a turbo at only 3# you'd still make more hp than the big bore and you now have the basics to add power by the turn of a dial. If you run at elevation your just bringing the sled back to what it would of been at sea level depending on boost pressures and elevation so is it that much harder on the engine? probably not. plus if your engine has issues or you throw a piston, at least you can opt to go with a re-man set of cylinders and new pistons of your sorts, big bore you're limited big time.
