High, high 13's, low 14's stock.

My '95 Z28 can take a '95 Cobra. Yeah.

Like what was stated above, Id watch out for the optispark distributor. Theyre a pain in butt, aside from that its usually little stuff.

my 1994 formula just ran a 14.4@97 with only a cold air intake and 113,000 miles. its a 2.73 rear end car with 245/50/ZR16 sumitomos. These cars are pretty fast out of the box.
As for mileage I don't drive a whole lot of highway, its alot of stop and go for me so I'm at about 17-18 with normal driving. Lead foot disease gives me 15-16. My personal best was 20.

so i have a question. I have a 95 z28 and did it come with 275 or 285 horses, i know that i have a single cat. but, 95s are sweet and the best year.

my 1995 has the OBD II connector under the dash, the car was bought by the previous owner in january of 1996 so maybe they just started puttin OBD II in them later that year?

No, it's still OBD I just with a OBD II style connector. Don't ask me why? I have no idea.

My '95 Z28 has 275 horses. '96 and '97 had an additional 10 horses because of the dual cat exhaust.

no, even tho you have the OBD2 connector, you still have OBD1!
that is a common deal on the 95 cars, OBD2 didnt make it into these cars til '96

'95 seems to be the most popular year, vented OPTI, OBD1, best of both worlds

P.S. dont be skeered of a '96-'97 car tho OBD2 stuff aint that much harder to tune, its just taken longer to get the cheap tuning software out for it but thats not much of a problem anymore
you might like the '97 interior better also....
get what you like and dont settle on the 1st one you drive unless it turns out to be the best of a few!

good luck and welcome to the f-body community (if thats what ya buy) :)