The accurized Colt will be a fine p'dog rifle...accurate as you need. Slap a good varmint scope on there, and marmots everywhere will fear your name lol.
You don't need a chrome lined bore for a 'dog gun...or anything else if you expect to be able to clean the rifle regularly, and don't plan on spending the next year in the jungles of Thailand.
The faster twist enable you to shoot heavier bullets...1/9 will handle just about anything you'd ever think about sending towards a prarie dog; if you plan on shooting 600 yard matches, you will need the heaviest bullet you can get, so the 1/7 would be better. For general all around shooting, the 1/9 is fine. 1/9 can handle 69 and 70 grain bullets very well, so that's all the twist you need except under very long range conditions. The 1/7 *can* spin lighter bullets literally into oblivion, disintegrating well before they reach their target. If you want to shoot 40gr bullets, the 1/7 might be a little too fast. I would expect the 50 and 55 gr bullets to be the varminters choice, 1/9 seems the perfect choice there too.
The RRA varmint rifle is indeed very nice...I had a 16" varmint upper, and it was a quality piece.
It lists for $975, so you could probably get it for under $900 easily.
You'll enjoy whatever you get, so have fun.