I have two custom, one semi custom, and a Cooper Phoenix. They are all good. Most smiths will guarantee a one minute of angle, very good gunsmiths guarantee 1/2 minute of angle. My experience is those gunsmiths who guarantee 1/2 minute normally produce rifles that with good ammo produce 1/4 minute of angle. I would lean towards custom so you can pick your rifling twist. 9 1/2 inch twist will stabilize the 175gr with no problem, and maybe even heavier, but I would pick a one in 9 inch to stabilize the 180, and even 185 gr Berger VLD's. Ballistic coefficient is a good measure, and anything with a ballistic coefficient above .650 will normally require a one in 9 twist. If Cooper has that in the rifle you want, then go for it.
Edit:
http://cooperfirearms.com/jackson-hunter
Nice looking rig.
If you download their Catalogue page 21 shows the twist rate for the 7mm STW at one in 9 inches. Couldn't go wrong with that rifle.