Lots to chew on. A few of my thoughts.

The Kimber is a lightweight rifle - even the LA 84L is going to weigh 7 lbs or less, the SA likely 6.5lbs. I had a Montana in 300 WSM when they first came out. I discovered it sucked with full power loads - this is the level of recoil I'm trying to avoid while going to lighter rifles. I have a Ruger UL in 30-06 - bares bones just the rifle/scope it weighs a shade less than 7.5 lbs. It doesn't bother me from the bench at all. I currently have a 7 WSM that weighs ~ 7.5 just bare rifle/scope. With my 160 gr loads it is tolerable. In a 7lb rifle its not going to be a picnic - which is why I said what I did on the 280 AI. I'm thinking cartridges from the 30-06 on down are doable in light rifles. For comparison, a 280 AI in a Montana will recoil 29 ft/lbs, 270 about 23, 25-06 about 21.5, the Kimber 300 WSM about 34.

On bullets, I'm leery of light for caliber bullets at warp speed. I've done that with various 7mm's through the years and they produce a mess at close range. I also tried TSX's and found them less than satisfactory - at least in the early days. Many love them, I'm trying to warm back up to them. I've had 7mm 140 and 25cal 100 act like they didn't open. The TTSX may be the answer. I really like Partitions but not all guns shoot them well. From shooting woodchucks, I've seen the effects of wind on less than slippery bullets. Low BC bullets drift alot with a bit of wind and 300+ yards. I'll take a few more inches of drop to lessen wind drift.

Of everything mentioned, I like the 7mm-08 idea with 120-140 gr bullets. What vels are you guys getting with 140 AB's and 22-24" tubes?

I've also run some numbers this AM on the plain ole 30-06 shooting 150 AB's. It hangs in their with the cartridges mentioned.

Adversity doesn't build character, it reveals it.