The 20v setup is weak on the whole... the silvertop ones have flow issues, the blacktop ones are much better.
You can do turbocharging on a 20V but you'll have to uprate the internals and it's still not the world's most ideal engine as the valves are fairly small... you can't really go bigger than standard with the valves because it leaves such little meat in the heads.
All depends what you want.... a silvertop or a black-top engine with a nice set of forged pistons, H-Beam rods, a porting job and a bolt-on low-blow turbo kit could make 250bhp or so nice and tractibly and still be nice and reliable

If you're after mega horsepower with a turbo, you'll start to push the limits and start breaking 20v heads and you'll be better off with the 16v