The polygonal rifling is supposed to offer a better seal between the projectile and bore resulting in increased velocity. In the real world, the difference is usually negligible and may not be worth the added cost for you. Noveske barrels are expensive and there are barrels that will shoot just as well, if not better, for less money.
The biggest question is whether you are up to the task. Talking about shooting accurately at distance is one thing, actually doing it is another. I learned that the hard way. If you want an SPRish build, it's going to depend a lot on your preferences. Actually, I've been shopping for a barrel for a build that I'm getting ready to start. Just waiting for the funds to show up. I just build a "field" precision rig, and now want to build an all out precision rig. This is my shopping list.
BCM SS410 18" barrel - I'm going with this barrel because I know they are good and very reasonably priced. I don't plan on single loading really heavy bullets and will load everything to mag length, so the 1:8 twist is fine for me. It has a rifle length gas system, which will offer smoother operation. I'm not worried about the reduced dwell time because I'll only be shootng full power loads out of it. My 16" middie build based on this barrel shoots sub MOA, so I figure that the 18" should too.
Vltor MUR upper receiver - I'm using this, well, because I've never done so. They are supposed to be "it." Tight tolerances so there isn't too much slop in the operation of the bolt group. Everything should stay in line, promoting accuracy. This upper is also supposed to be really rigid, also promoting accuracy.
BCM bolt/carrier group - just because I'm a fanboy. Good bolt group.
Spike's lower receiver - because they are built well, show clean machine work and I think the Spider with the red color fill looks really cool.
Geissele DMR trigger group - I don't think I need to explain this choice except to say that I prefer a two stage on a precision rig.
Magpul PRS - It's a good stock and I don't have one right now. This recoil system should work nicely with the rifle length gas system and you can get that neat mono pod attachment for it.
Bushmaster free float tube - I use these tubes because they are light and comfortable. I have no need for rails on a build like this. The bushmaster tube uses a really thick nut which helps with rigidity. It also comes with a bipod stud installed.
I think that this will be the makings of a tack driver.