The .270 Weatherby Mag is well known as a long range deer rifle. The .270WSM's velocities come pretty darn close to the Weatherby Mag, so there is no reason to doubt the .270WSM's long range capabilities. The added benefit of the .270WSM over its Weatherby counterpart is that the WSM approaches Weatherby velocity while having less powder than the Weatherby - thus having less recoil and, in turn, thus enabling you to shoot more accrately.
As everyone on this board probably already knows, I absolutely love my Tiikkas. However, there is one thing that you may want to consider. Apparently, Tikkas, at least in the WSM cartridges, deliver lower velocity that other gun manufacturers.
There was an article once specifically on the .270WSM in both a Tikka and a Savage. With the same loads, the Tikka rifle produced velocities about 200 fps LESS than the Savage. That's a noticeable difference. You might as well shoot a .270 Winchester and get the same velocity without the recoil.
Additionally, other board members have chrony'd their Tikkas in, I think, .300WSM, and have similarly found the velocities to be noticeably lower than they should be.
There is no doubt that Tikkas are accurate. However, if the Tikkas WSM rifles are much slower because of their long throat, then, accuracy or not, to me it doesn't make sense to get a Tikka in any WSM cartridge.
Zachary