I would not run anything less than 4.56's with a t-56. I say have it checked out by a mechanic and if it is in good shape, go for it. Read up on these cars here on the forum. You will not use gobs of gas unless you get on it a lot which you will be tempted. If you drive that little to work and back, get out on the weekend and drive it. Short trips like that are bad for your car. Also, both 5th and 6th are overdrive gears so your 4.56's will be fine on the highway. I wish I had that setup. Good luck and have fun.
'95 9c1, pcmperformance.com 93 tune, Dynomax Ultraflo catback, K & N box filter, LT4 KM, 160 stat, 3.08 Posi.