The new exhaust system works as well as it sounds. Mid-range power is noticeably improved. Removing all three catalytic converters helped, no doubt
It runs well at all speeds with the stock ECU - no pre-ignition ping and the engine runs at the same temperature as before. Fuel economy is roughly the same; maybe a bit worse but not enough to change my 120 mile range for the low fuel light to come on.
Having said that, though, I think performance-wise there's room for tuning. A Power Commander or something like it would make the thing downright dangerous. So of course I'll add one when I get the cash.
But the main benefit has been in handling - loose ten pounds of stock exhaust and wonderful things happen...
Best mod evah.