Ratio

Depends. Are you going to be in the mountains a lot or just on flat roads? As a general rule, Higher gears (lower number) typically have a lower RPM and will get better MPG on flatlands but are going to be rougher in the hills. Lower (bigger number) gears tend to be better in the mountains or if your always heavy as the engine wont need to work as hard.

Theres some variation in there of course but you honestly wont notice a huge diffrence between 3.07 and 3.55 most of the time. But i also mostly do vocational with a manual and know very little about volvos overall. That said the 3.55 are a pretty common choice for a reason. Namely they give a good well rounded result. 3.28s are also fairly common if you can find them.

 

It is more of a package. Knowing the transmission ratios and final is just as important.

you can put a 3:08 or. 3:55 in the differential.
The 3:08 will be best with a direct output, the 3:55 would be better suited to an overdrive.

 

Tire size matters, too. I'm running 3.08 with 13 over but tires are only 36" tall. That's equivalent to 3.55's on tall rubber.

 

Good for you. Now answer the question @Arctic_fox asked, otherwise, everybody's just guessin

 

What’s the torque curve on a 2011 Volvo engine? Is it designed to be run at 1000-1200rpm or do you need to be cruising at a higher rpm? What speed do you want to cruise at? What’s the final ratio on the transmission? Which rear end will put you at the best rpm at the speed you want to cruise at? Lots of things to think about other than just rear end ratio.

 

Will you be on the Interstate, or doing a lot of stopping and starting?

 

307 and 68mph or less
Without knowing all the other important stuff.