Just some random thoughts...
My friend has a .300 RUM and put a Vais muzzle brake on it. He says it tamed the recoil pretty significantly. Might be something to think about.
I plan to get into long range shooting, 500 yards plus, and I am sure both rounds are capable. I am also a hunter for deer and the occasional moose in which both these rounds will also cooperate.
What are your intentions for the rifle specifically? I see the potential for hunting but, "long range shooting", do you mean targets? I would only consider the Ruger if it's going to be a hunter only. Ruger accuracy upgrades are very slim if you want it for targets. The Savage has a lot of aftermarket parts available if you decided you didn't like something about the rifle, wanted to improve it, change calibers, I could go on and on. Personally, if there's to be more target work than hunting, I would buy the bare Savage target action and build the rifle up instead of going with a factory rifle offering...but, that's just me.
As has been pointed out, the conventional wisdom on the 6.5x.284 is that it has a 900-1200 round accuracy life. That's benchrest accuracy. You would still be able to hit a deer/moose/whatever beyond that number. How many more rounds, who knows. Everybody I know shoots benchrest and replaces them. Hot loads, cleaning technique, allowing for barrel cooling,etc. will all play into the barrels' life expectancy. I've got three rifles in 6.5x284 Shehane (improved version), all are approaching 900 rounds, so I'm watching to see when the accuracy will fall off. They are benchrest rifles, not hunters.
In the longrange benchrest circles, a lot of guys are switching over to the straight .284 Winchester or an improved version of it. Barrel life is expected to be over 2000 rounds and the 7mm bullets have better ballistics than the 6.5's. You'd be able to use heavier bullets going 7mm vs. 6.5mm which might be of interest when hunting. More expensive though and a bit more recoil. I'm having my lightgun rebarreled right now in .284 Shehane and having a muzzle brake put on it (a first for me).
I've never shot a 6.5x55 but read the accuracy is supposed to be good with a little better barrel life than the 6.5x.284. Lots of 6.5mm bullet choices out there.