From research the 2.45 will give better off the top bump compliance and the 2.65 will be better for large hits for jumps.

That is not true. These are coil springs of the same weight. So long as they're preloaded the same and the coils don't bind when compressed, they will act exactly the same.

The 550x2.45 will be a little lighter (not really a concern with an eMTB, so assuming the 550x2.65 will fit your shock, run whichever one you can get faster/cheaper.

 

Linear coils are actually slightly progressive, so the shorter coil may be marginally more supportive near bottom out. I doubt you'd be able to feel that, though. If you could feel any difference at all, it's more likely the variation in spring rate from the wide manufacturing tolerances than anything else.

I'd go with the 2.45 just because it's probably a bit lighter. Just keep the preload to a minimum.

 

Get the 2.65 active length. I do not like being so close to block height with spring lengths for any given application. As mentioned above, there will be virtually no difference in spring rate/feel between the two, other than that fact that fox SLS springs have terrible rate qa/qc.

My real suggestion would be to buy a spring from super alloy racing as the rate control is better, and they are black.

 

My real suggestion would be to buy a spring from super alloy racing as the rate control is better, and they are black.

SLS springs come in black now but yeah, SAR would be my 1st choice too.

OP - Consider buying a cheap spring first as you might need try a couple different rates to find what you need. Spring calculators are just a starting point. Once you get right rate, can send that spring to SAR. They will dyno it to find what the real rate is (since actual can be way off from what's printed on the spring) and provide their high quality lightweight spring that matches closest to the dyno'd rate.

Cheap spring example:
FOX Steel Rear Shock Coil Spring - 550 lb. x 2.8" Spring Travel, 5.75 TLG (Total Spring Length), Black

 

Fox recommends 67mm springs for 60mm travel shocks, guessing because if you crank down preload on a 61mm spring it could end up being too short and coil bind. I always run the slightly longer coil, weight is minimal.

 

Great response's, thank you all! super helpful.

 

Use this spring rate calculator, it's proved reliable time and time again, BUT only if you use springs that are guaranteed to be accurate, some orange ones are NOT! Spring Calc