Some rules of thumb.... when asking about brass, it fits into 2 questions...
how tough is the brass? ie, how well does it stand up to loading and what pressures can it tolerate before the pockets open up...
how consistent is the case volume? Case weight is NOT a good indicator of this.
Lapua is typically regarded as the toughest brass on the market (some of the thickest as well). This brass can take a beating and handle many reloads, even if loads get a bit toasty. But since you are asking about 6.5 CM brass, you have look at how the market is responding to the brass.
here, we see that many brands are making excellent quality brass - dimensions and case volume. At SAAMI pressures, most everything is working great and lasting well.... so, it now has more to do with preference then brand x working better then brand y. At least to the 1/4 MOA level.
SR vs LR... simple, do you shoot in the very cold? do you want just one load option throughout the year? If yes to both, then go with the LR. If you are going to run hotter then SAAMI loads and keep them in weather above zero, then the SR will work.
As a note, I have yet to see a 6.5CM at very high pressures shoot as consistently as a load within SAAMI specs. There might be some out there but of the several I own or have direct hand in load development, haven't seen it.... we are confirming at 1000yds and beyond.
YMMV
Jerry
Note: as a dealer, I offer pretty much all options so I have no preference in any direction. This is just my experience shooting this chambering over the last 2 yrs.