b18b/b20b/turbo?

I was just thinking about this, and I wasn't sure if it was worth doing or anything. I'm not a motor guy, so I thought I'd ask here - could you do this, and would it yield better results w/ turbo than b20vtec w/turbo, or is it just a stupid idea?

(Yes, I know I posted this in two forums, but I got absolutely no response in the motor forum).