The EFI even on the 340 would seriously tone down any driveability issues and should help the fuel mileage. I got about 2 mpg with the EFI and an additional 2 with the T56 Magnum.
I didn't even get remotely agressive at tuning mine for fuel mileage, I rarely drive for more than 1/2 hr at a time, most roads in the 45-55 mph range with quite a few stops (with sometime between 25 and 35) and I'm basically always getting between 14.8 and 16 mpg. Given that I tuned it myself, I could still be leaving quite a bit on the table, but it stays in range a lot better than my 750 Quick Fuel double pumper did.
I'm hoping next year that I can do either Power Tour (depending on where it starts and ends) or maybe do MoParty (my folks live about 1 hr away from Bowling Green in TN). Have to add A/C first I think though. I'd be fine at least doing the autocross. Would be driving it there and back too...
I look at the viper calipers once and a while, but I'm really unsure if the opposed pistons have any chance of clearing my Torque Thrust M's. It's somewhat difficult to offset the rotor far enough in for the caliper to clear. I still have a lot of stopping power at my disposal with the cobra brakes + hydroboost. No idea what pads are in those either, probably should see if I can still read the edge codes. For the street, I would imagine you'd be best to run a low met of some sort, hopefully with a GG edge code. Sometimes another option is Raybestos Element3 pads that are GG edge code but they are a combination of low met and ceramic, a little less dusty and still quiet. Use them on all the "normal" cars and they are usually a good upgrade.
I find the other side of these brakes kind of interesting, during street driving, I really never get any heat into the rotors, I come back from a drive and they are rarely over 130F where my regular cars are usually in the 210F range after a drive.