There is actually a very large difference between the two. The SOHC VTEC only has the variable affect on the intake side (there is only so much room on a camshaft). A DOHC VTEC has VTEC on both the intake and exhaust cams. The DOHC does, has a bit of an advantage because of this, but is also much more expensive (a lot more parts to support and contol that second cam), heavier (ditto) and as far as I knew, made less torque (it takes more engine effort to turn two cams) but I'm not positive on that part.

Also, another big difference is the fact that Honda builds the SOHC to be lower performance engines. The SOHC engines (even the VTEC one's) are found in lower model Civic's and the DOHC VTEC engines are found in the upper level Civic's and Integra's. If Honda were to build a SOHC VTEC engine with the same high compression, aggressive cam and fuel tuning to support 8000 rpm and a similiarly geared tranny to a DOHC VTEC, the SOHC would most likely match the DOHC's numbers. Problem is Honda doesn't do that. They're more concerned with emissions and milage with most SOHC engines because there put in cars that are sold to people (for the most part) who are less concerned with performance and more interested in mileage and reliablity.

By the way, just so you know, Corvette's don't use DOHC engines, they still use pushrods engines. The SVT Mustang Cobra is a 5.4L DOHC engine and it is impressive. Seeya.