No experience with Hodgdon Benchmark, but it wouldn't be my first choice.
Hodgdon Benchmark:
As the name implies, this Extreme Extruded propellant was developed for precision cartridges. As such, it is ideally suited for benchrest and small varmint cartridges like the 6mm PPC, 22 PPC, 6mm BR, 223 Rem. and 222 Rem. Additionally, it performs superbly in the 308 Winchester with light match bullets like the 147 gr. and 155 gr. versions.
From this description, it appears to be aimed at light, fast bullets, and 6.5X55 bullets seem typically to be heavy and slow. The one reference to a .308 is a relatively light bullet. It might work well in the 6.5 Swede, but, again, it wouldn't be my first choice.
I'm looking past RL22 lately. My five-shot groups usually (but not always) started out well, then through the session they'd begin to get bigger. I blamed technique, but it might not have been.
There are two other powder possibilities. First, RL22 is a double-base powder, and some folks do have trouble with consistency with that kind. Second, RL22 (and all of Reliant powders, except RL15) are temperature-sensitive, with velocity changes directly related to ambient temperatures. Load at 70 degrees Fahrenheit, and if you shoot at 30 degrees you might lose as much as 200 fps; shoot at 90 degrees and you might be looking at a pressure event. At the very least, your finely-tuned load is no longer finely-tuned.
To fix these possibilities, I've decided to develop some loads using single-based, temperature-insensitive powders - Hodgdon'e Extreme line. I'm trying H4831SC (because I got it cheaply), but H4350 might be even better. No accuracy results until this weekend, however.
Jaywalker