5.14 ratio to 4.10 or 3.90 for 1 Ton Rear End

[TreverSlyFox]

My 71 GMC 1 Ton 7200 lb axle has a ratio of 5.14 and I get about a top speed of about 65 without really pushing it. I see that you can get a 4.10 or 3.90 ratio ring and pinion now for $350.

I've got a 4 speed tranny with granny 1st gear, if I made the swap what kind of top end speed could i expect? I'ed like to make Hi-Way speeds of 70-75 but which ratio will do it, the 4.10 or 3.90?

I imagine my speedo would be way off and have to be re-calibrated.

Anyone out there done the swap on their 1 Ton? Are you happy you did it?