It was settled years ago that poly barrels dont shoot any better, or last any longer than standard barrels.  They shoot as well as any other button rifled barrel, which is usually better than the person pulling the trigger is capable of
  If anything poly barrels have been shown to be more  finicky about bullet choice.  Some bullets dont seem to shoot  well at all out of poly barrels.  

Quoted: Bigbore, I'm really interested in your comments.  I'm curious if you have any sources you can refer me to?  I've been reading all day about the differences and the claim that poly barrels last longer is based on the fact that the absence of traditional lands and grooves helps evenly distribute friction between the barrel and bullet, thus allowing slower erosion.   Sounds reasonable I suppose, although HK claims something like 5X over a conventional barrel. What about velocity gains with poly barrels? Do you think that is accurate? Any comments would be appreciated.

Post this over in the competition forum, or over at long-range.com.  
Competition shooters were playing with Poly barrels back in the M-14 days.   Do a search on Sinister's posts here - he and his crew never saw any benefit to poly barrels which is pretty much everyone elses results. No velocity gains either.
Heat kills barrels by bruning/cracking the throat away, the absence of traditional lands and grooves doesnt matter; anyone who tells you different doesnt know any better.

I personaly know some High-Masters who bough T2Ks w/poly barrels and each of them was burnt out by 2K rounds.  None of those guys replaced the barrels with poly barrels.

The only Service Rifle I know of with a poly barrel wouldnt shoot the owners 80gr. bullets, so he only uses that it for rattle battle now.

Flip a coin, get what you want, you'll never know any difference.
I think this latest fad is just marketing hype, which cant be proven either way with a battle carbine.