I would way rather have the gearing of the T-56 than that 6 speed automatic. The rpm drop between 1st and 2nd of the 6l80e/6l90e trans is even larger than the wide ratios of the 4l60e/65e/70e trans.
The best stock auto trans that GM ever built in regards to gearing is the thm-200r4. It has a:
2.74:1 1st, 1.57:1, 3rd 1:1 4th(OD) 0.67:1. Its got a 1st gear ratio that is bang in between the 700r4/4l60e and the thm 400/4l80e, 1st gear ratios, and it has the highest OD ratio of 0.67:1. Has teh best balance of 1st gear acceleration/traction, gear spacing and low rpm cruiser. The 80e would be perfect if it had a bit lower 1st gear and a higher OD ratio. The low 0.75:1 of teh 80e/85e does its job in teh application it was designed for, having the lower 0.75:1 OD ratio helps with OD towing. The cruise rpm differnce between the 0.75:1 thm-80e/85e OD and the 0.67:1 thm-200r4 OD ratio is 234 rpm at 70mph with 30" tires,3.73 gears.
700r4
3.06:1, 1.63:1, 3rd 1:1, 4th(OD) 0.70:1
4l80e/85e
1st 2.48:1, 1.48:1, 3rd 1:1, OD 0.75:1
6l80e/6l90e
1st 4.03:1, 2nd 2.36:1, 3rd 1.53:1, 4th 1.15:1, 5th 0.85:1, 6th 0.67:1
T-56 (F-body Camaro/Firebird)
94-2002 manual (torque rating of 450 lb/ft)
1st 2.66:1, 2nd 1.78:1, 3rd 1.30:1, 4th 1.00:1, 5th 0.74:1, 6th 0.50:1
1993(1st year of T-56 use in the F-body, lower rated torque of 400 lb/ft)
1st 2.97:1, 2nd 2.07:1, 3rd 1.43:1, 4th 1:1, 5th 0.8:1, 6th 0.62:1
T-56 from the 93-02 F-Body is the same length as the 700r4/4l60e/65e/70e and uses the same transmission output yoke, therefore when swapping in a T-56 from an F-body, the stock driveshaft and yoke can be reused. The very high 0.50:1 6th OD gear can allow for some very very low rearend gears. There was one guy that swapped a T-56 into a truck and he was running 5.13:1 rear gears and still cruising at 2000rpm at 70mph. I dont recall his rear tire height exactly, but if I run the numbers a roughly 30" tire is needed to cruise at 70mph revving 2000rpm. Guys that are running stock rear end gears report that 6th gear becomes useless in any situation other than fast highway cruising as the rpms are much too low, and the engine lugs.
3.73 gears, T-56 OD in 6th, 30" tires, 70mph revs at 1462 rpm
same but for
2.41 945rpm
2.56 1004rpm
2.73 1070rpm
3.08's revs at 1207rpm
3.23 1266rpm
3.42's is 1341 rpm
3.73 again is 1462
3.90 1529 rpm
4.10 1607 rpm
4.11 1611 rpm
4.30 1686 rpm
4.56 1788 rpm
4.88 1913 rpm
5.13 2011 rpm
5.38 2109 rpm
5.57 2183 rpm
I realize the attraction of having more gears in a trans, but I am not 100% sold on these 6 speed autos. They are getting better though, just as everything that is new, it takes a while to iron al the bugs out.
peace
Hog