ZCat3,
yes, depends what gear the turbo is in, and if it is on boost or not. i thought when you said "high speed runs", i thought you meant "very" high speed

, not 60mph roll-on
myself and a fellow in a mid-late 80's slant nose played around a bit on a drive last summer. I am not sure if he had any mods ( but i am sure it wasn't de-tuned

) We went through all kind of conditions, speeds, altitudes, etc.
the cars were quite evenly matched. if he rolled on the throttle when on boost, he'd pull on me. we were close until boost came on otherwise.
it was a very hot day...so that probably helped me.
I am not sure of his mpg, but i was very impressed with the 993. flogging the car hard, with miles and miles of 130-150+ mph, i probably got better fuel mileage than my SC at any speed
One thing that the cars have in common...they are both a lot of fun.
one big difference- it costs a LOT to make a 993 go a little faster, if you spend a lot on a Turbo, it will be a LOT faster!!
cheers,
Max