What is your idea of "lightweight". Reason I ask is because a Rem700 with a hvy bbl and decent scope is gonna be over 10lbs easy even with a 20" barrell. It will probably weigh even more with a chasis system like in your link. MY springfield loaded m1a weighs in at 10.2lbs unloaded. The springfield scout model probably saves a few lbs so you may want to look there. Most Ar10s are in the 10lb range as well. My friend has a dpms with a 16 bbl and its pretty heavy and obnoxiously loud even with ear plugs. The big question is what do you plan to really do with rifle. If its mainly going to be used for hunting from a stand the ar10 or Rem 700 will be easier to put glass on. If you do a lot of stalking up and down mountains I wouldn't want anything over 8lbs in a dedicated hunting rifle.
Kill em all and let God sort em out! USAF