[Overdriven]

I used 15t with 37/13 and 17t with 43/13 since that's what you said you wanted to run. With 37/13 + 15/68 you get 48km/h, 23.65:1 fdr (final drive ratio), and 11.36 axle torque. With 43/13 you get 47km/h, 24.25:1 fdr, and 11.65 axle torque. So my point about axle torque being dependant on fdr is correct, and changing to the 43/13 diff ratio requires changing the pinion by 2 teeth to maintain the same speed and axle torque. Although I think there is a language barrier thing or lack of explaination going on contributing to the confusion.

I say go with 43/13 over the 43/10 because of gearing options. With 43/10 you'd need 54/22 gearing and 6s to get to 45mph (70km/h). With 43/10 diffs and the 17/68 gearing you said you wanted to run, top speed was around 20mph. But maybe you're okay with that. Either way I hope our answers have helped in your descision making process.