Let me break it down..........
When you do the gears your speedometer will be off, so if you are going 65mph it will read 80 (as it was in my case with 4.10s). So you need to correct that, you can do that with the programmer or the sct tuner.
When it comes to actual mph.... You are aware that when you install those gears every single one of your gears shortens also right? Its not just throw them in and be fast all of a sudden. In my personal car with 4.10s my 4th gear (5 speed manual) redlines at 110mph, so anything after that i am in overdrive, which is useless. My speedometer goes all the way up to 150, but i won't get there unless i change out the gears again or i do head work and up my redline to 7k. Hell even with stock gearing my car has a hard enough time getting to 130mph.
So how fast you will be going will depend on a lot of factors. Yea, it will be easier to get up to that higher speed with the 4.10s than stock gears, but you have to take in other variable into account.