I've used it with temps 40-60 some degrees, so can't help much on your
question. I've looked all throughout many forums since the announcement
of RL17 and found no statements about it being temp sensitive. If it were,
surely, someone would have complained.
The only complaints I've come across, were that it doesn't produce quite the
speed claims made, and have found that to be true in my loads. Even at that,
it has given me the best accuracy of many different powders in my Sav .25-06
26" barrel. Pushing an 85gr Nos BT @ 3500fps with accuracy is plenty
satisfying to me.