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OP: Mine is the T56 Magnum with 2.66 first, .80 5th and .63 6th.

To xb-60, what ratio is the 1st gear on your toploader? the close ratio has a 2.32 first gear and the wide has 2.78. I generally agree with your speed is really like a 5 speed given your gearing; but I would still recommend a five speed; your 2.92 is a nice 60-70 gear but not really a cruise gear; if you a doing 75 on the highway for a decent stretch then a 5th gear would be nice.