Basically the rear bridge of the M7 is .5" shorter than the M700. The bolt and firing pin are shortened as well. It will be a couple ounces lighter than a 700, not much but if shaving ounces is your priority, its a good deal.
I am almost finished building a rifle, that fits your decsription.
Its a M7 with a 25" Lilja chambered in 7WSM.
With a Lone Wolf stock, Talley rings, and a Nikon 2.5-10 Monarch it will weigh less than 7 lbs.
Although I really like the WSM, I should have gone with a 7SAUM though due to magazine length restrictions of 2.80". The mag can't be extended on a M7 because the trigger housing is right up against the factory mag box.
The SAUM is a great cartridge that fits the M7 just right. My wife has a factory 7 in 7SAUM that will hold MOA out to a couple hundred yards. You can fit 162 a-max's in the mag, and get to about 2900 fps with a 22" bbl. This gun needs a quality stock and it would be a near perfect mountain rifle.
If it were me, I'd get one of the stainless/synthetic 7SAUM's and put it in a Lone Wolf/Manners/MPI..etc. stocks. It would be a light, handy gun with some punch.