I have no clue what my MPG's are at 120mph...lol...I try not to sustain those speeds for too long,...I have no idea what IROKS are speed rated at,...but I'm damn sure it isn't over 110mph
And as for MPG's.....I gave up on MPG's LONG AGO.
This is my Motto:
MPG's are like having sex when you get older,...don't b1tch about how much you get,...because it could be worse.
As for gearing...I had
3.73's and 36's
3.73's and 39.5's
4.56's and 39.5's
4.56's and 41's.....which is prefect for me.....@ 80mph I run 2,250rpms