You can get a Tremec 5 speed with either a 0.82 fifth or a 0.64/0.68 fifth gear.
An LS1 T56 comes with a 0.74 fifth gear and a 0.50 sixth; the aftermarket T56 and some earlier LT1 T56's come with a 0.80 fifth gear and a 0.62 sixth.
Both the T56 and the TKO 5 speeds come with a 1.0 fourth gear.
So with a TKO using a 0.64/0.62 fifth gear you'll have a bigger drop off from 4th to fifth and a higher numeric (lower overdrive ratio) top gear as compared to an LS1 T56. As compared to the aftermarket T56, you'll simply have an extra gear between 4th and your top gear.
IMHO, the 0.50 sixth gear in the LS1 T56 is useless with a rear lower (numeric) than 3.55, and even that is marginal (roughly 1400-1450 rpm @ 60mph). With a big cam engine that could be pretty unpleasant.
On the other hand, the 0.5 sixth gear can tame 3.90's and 4.11's for cruising. Even with my aftermarket T56 with the 0.62 sixth, I was getting roughly 17.5 mpg on the freeway in my 350 '68 Camaro. I recently swapped in an LS1 T56 and I'm hoping to see 20 mpg.
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