I've got both a Ruger Precision Rifle and a Tikka T3x Tac A1 – both in 6.5 Creedmoor.
The Ruger shoots tighter groups than the Tikka. Noticeably tighter. I've tried pretty much every combination with the Tikka, but I can't get it to shoot on par with the Ruger. The Tikka isn't an inaccurate rifle by any stretch of the imagination, but the Ruger outshoots it easily.
The only problem is, the Ruger shoots 10 inches to the left at 100 yards, and with a scope like a Nightforce NXS 12-42x56 you only get 30MOA of total windage adjustment which works out as a 25/5 split instead of 15/15. I suspect (hope) that it's an issue with the scope rail, rather than a barrel/receiver alignment issue.
The Tikka feels like a slicker, tighter gun – but the CTR style magazine simply doesn't work reliably enough. I haven't been able to get it to feed a complete 10rnd set without encountering an issue. I reverted to single loading shortly after buying the Tikka. The Ruger/PMAG combination works flawlessly – I've never had a single problem with it.
The Tikka rusts like a pig, regardless of how anal I am keeping it dry and maintaining it. I'm not alone. I've yet to meet a real world Tikka owner who hasn't suffered the same problems. Bear in mind I live in Scotland, and four seasons in one day is the norm.
The Tikka is pretty much a done deal straight out the factory. You'll struggle to replace the rear stock with any great effect, and likewise the pistol grip is a kind of half beavertail affair. The cheek height adjustment is rudimentary and not particularly repeatable, and the length of pull requires disassembly/spacer installation. The standard rear stock on the Ruger offers tool less cheek height and length of pull adjustment, but in practice it can be quite an awkward affair. The Tikka also offers butt pad height adjustment, something which the Ruger lacks.
With the Ruger, you can swap out pretty much everything. I find the Magpul PRS rear stock works really well with the Ruger's in-line barrel axis/buffer tube design.
The Tikka has the better factory trigger of the two, and the standard Tikka pistol grip is very nice indeed. I swapped out the standard Ruger trigger because I wasn't happy with it, and likewise I didn't like the standard Ruger pistol grip either. The safety lever on the Ruger is beyond terrible.
All in all, I'd swap the Tikka for another Ruger, but I wouldn't swap the Ruger out for another Tikka. If you're keen to go down the Tikka route, I think you'll be far happier in the long run if you buy a Tikka T3x barrelled action, and drop it in to something like a MDT chassis. This will allow you to enjoy the action, without being crippled by the Tikka CTR magazines. Ultimately however, the in-line recoil path of the Ruger is a superior design, and it feels a bit like comparing VHS/Betamax (Tikka) to DVD (Ruger).
I hope that's of some help...