70-75mph with the 200-4r and locked torque converter.
The clock doesn't lie, this thing is sloooooow to 60+mph, but it feels and sounds like a rocket ship the whole way! Going back and forth between my Skylark (w/ ~500-550HP,455, 5-speed, 3.89 gears) and the Firebird, is night and day. I blink in the Skylark and I'm doing 60mph, Firebird takes just shy of 12 seconds, but its fun getting there and sure seems closer to 8 seconds, but a dozen measured tests say otherwise. I'll be putting the bigger cam in this May. The factory rated the bigger cam at 40 more HP than the small cam, but that also came with a compression boost I won't have, and I may have of already gotten some of that with the 4bbl intake and dual exhaust manifold. That rating is a 22% boost in HP, I should be able to get probably 15% of that. After the cam is broke in I'll install stiffer valve springs for a bit more rpm. At that point I should really be able to tell the difference.
The real mpg test will be at the end of the month when I take it on a 1200 mile trip.
Rebuilding an OHC Pontiac 250 with EFI and a Turbo