Depends what you want do do with it. I have both a 1:7 and a 1:10, I shot 5000 rounds last year through a 1:10 twist, mostly 55gr, and then this year so far I have about 1300 mostly 55gr through a 1:7 twist.
I am mostly tactical shooting, and personally, with the way I am shooting I do not notice a difference between the two twists while shooting 55gr, out to about 200yds sometimes 300yds, 55gr ammo shoots fine out of both my 1:7 and 1:10.
The non restricted 1:7's are made strictly for export and are meant for shooting heavier rounds. If you want to shoot those heavier 70gr and higher rounds accurately out to extended ranges, like 600+ then get a 1:7, most people say that the highest you should go in a 1:10 is about 63-64gr, where as a 1:7 should handle up to 80gr or higher if you can find it.
That being said I know some people have had good results shooting 77gr through a 1:10 so, it really depends on what you want to do with the rifle.
If your plinking and having fun, get either. If you want to go long range and heavy bullets, then go 1:7, if you want a Swiss Arms varmint, get a 1:10 and shoot 40gr all day.
The first time I took both rifles out together I wanted to compare and Shooting 55gr American Eagle through both the 1:7 and the 1:10, with iron sights I was able take out pop cans at 220yds like nothing, with both rifles. That suggests to me anyway that both twists handle 55gr more than accurately enough for me.
I have also shot a lot of CQB using 55gr through a 1:7 twist and never had any issues with stabilization.
