Gear Differential Question

Hi
I have done some research through over 50 pages of posts about changing gear differentials, but i still have a question.

Here is some background info:

I have a 77 Euro 350SLC with an automatic tranmission and a 3.46 differential.

The low end in the car is so powerful, i can burn rubber off my 8" rear tires. The acceleration is enough to pull my head back.
Not bad for a 20something year old car!
Unfortunately it takes 3000rpm to go 60mph, 4000rpm to go 80mph, 5000rpm to go 100mph, you get the idea.

I want to be able to get better gas mileage and to be able to go at high speeds without having to put such a high strain on the engine. I don't mind sacrificing the low end performance.

A person from a well known mercedes dismantler shop told me all 77 USA 450SL / SLCs came with a 3.07 differential as standard equipment. He said i may no see much of a difference installing a 3.07, and he offered me a 2.47 differential from newer 500 / 380 SLs

The question is: which differential should i install?
3.07? or 2.47?
Will i cause any damage in the long term by installing the 2.47?

Any help in this matter will be appreciated.
Thank you all for this great forum.

Yuri
Lovingly rebuilt 77 350SLC
Northern NJ.