Swap Disco II Differential to 3.08

So, kind of a noob when it comes to diffs, but what kind of issues could come from changing the gearing in the diffs to 3.08. Why would you want to do that you ask? I did a diesel conversion on my Disco and put a 2.8l International TGV mated to the ZF 4-speed. I am getting 20mpg city and hwy. The current 3.53 gearing keeps the motor turning at ~2500rpm at 70mph, the sweet spot is 2000-2100. If I swap to a 3.08 diff on both axles I will be churning at 2108 at 70mph. What could be the positives and negatives for doing something like this? Thanks.

Check with Ashcroft transmissions in the UK they have a hi ratio gear for the transfer case. Or if you are is the US try GBR in Utah i had my lockers re-geared (4.14) by them in the Disco D1 diffs i installed sometime back into my series 11A 88 inch