I own more rifles for my 7 mag. I don't really buy the "flexibility" thing. If I did much varmint hunting, I'd get a .22-250.
Your preference doesn't say much here. I also have a .22-250, a .22-250AI, multiple .223(s), and a 6BR. I also still carry 90 or 110 Gr .270 loads in the field. Read of the flexibility as was described in Pet Loads by Ken Waters, and contribuited to by T. Whelen, I claim to be no authority.
Regardless, it'll be hard to find much to say positive about 7mm Mag and it's suitability and flexibility for shooting light varmint bullets. Check a few reloading manuals, try a few loads. For .270 Win, you'll also find varmint offerings in factory ammunition. For 7mm Rem Mag, see if you can even find a good reload.
And on the heavier end of things, run comparative ballistics, 7mm Rem Mag is just a hair over 100fps faster, and 1" less drop with a common zero at 300 yards. Longer than that, you'll still need to account for drop with either. The 7mm Mag just has a lot more cost, noise, recoil, and a belted case for little in return for less than 200 fps @500 years, (even given the 7mm Mag's higher BC), and 10 grains or so more weight. Insignificant in my book.
http://www.remington.com/products/ammunition/ballistics/comparative_ballistics_results.aspx?data=PRA7MMRA*PRA270WA
I'll take the flexibility, over the cost and relatively insignificant increase in power.
I think both the math, and available references pretty much make my point. But like all decisions, make yours and live with the results.