all depends on the setup, single cam turbo's can be fast, but d-series motors are inherently weaker and require stronger rods before a lot of power is put to the wheels...plus the transmissions are weaker, especially the differentials.
in my opinion its not worth building a turbo single cam because of their tendency to break. yes, you can get away with it but this is only on lower boost and a gsr motor with bolt-on's will be just as fast...plus you'll have reliability and power that is always there.
now, single cam vtec's with nitrous are another story...and i'm a firm believer that the cheapest way into the 12's is a mini-me + 50 shot + gutted crx. this way, if you break things you can just replace the bottom end easily without having to worry about pipes, turbos, etc.