Now you're talkin'! One of my very favorite cartridges...and I really don't know why! The action needed for it is standard, so it ain't really "compact"...or "light". The velocities are enemic compared to a 264 Winchester Magnum (which is the same bullet diameter) and energy is just "so-so"!
So: Why the love? Because, like my 257 Roberts it just plain "does the job". Anyone in the family can shoot it, as the recoil and noise is easy on the shoulder and ears. It will drop anything at reasonable ranges that you are hunting (with appropriate bullets and loads).
Unlike Ken, I don't own a "one-holer" in this caliber. I have owned them. I sold off one of "2" SAKOs ever imported by Stoeger in 6.5X55mm made up as what they called a "Handy Carbine". But a "Bateau Matte". The "Handy Carbine" came in a SAKO "Finnbear" (long) action with a factory McMillan black glass stock and a medium-heavy contoured "stainless" barrel. I had it topped off with a straight 7X 56mm Kahles scope with 26mm rings. Someone needed it more than me...Gone!! I regret selling it but I do that a lot. The groups were almost as good a that Cooper. Mine was a repeater. I know a good many of the Cooper rifles are single-shot, hence another reason for their exceptional accuracy.
I've also had a Ruger M-77 in 6.5 that shot about an inch and half on a good day. A Husquevarna (spelling?) "Mauser-styled" bolt that was a little better and a Remington #700 "Classic" that shot less than an inch.
Currently I own a Steyr "Mountain Carbine" in 6.5. It is very lightweight, with a 20" barrel and synthetic stock, which is adjustable for length of pull, via removable spacers between the recoil pad and stock. It shoots 1/2" all the time with factory Winchester 140 gr. PSP ammo! Elizabeth uses it to terminate whitetails! Outstanding rifle! With the Fuginon 3-9X scope it's as versatile as you can imagine. Cannot address the lighter 120's in it. When I get down to that weight I usually use my "Roberts".
Best, Capt. Chris
PS: Here's Elizabeth with a 125 lb. whitetail doe shot with the 6.5mm. Here first deer!...CCS