With Varget and RL-15 in the mix another powder with similar burning rate with no temperature sensitivity (this is what Hodgdon says) is IMR 8208 XBR.

Hodgdon's reloading data center has this powder as the fastest with a 250 gr bullet in the 35 Whelen. 54.3 gr for 2515 fps

From description of IMR 8208 XBR: "shooters will find IMR 8208 XBR totally insensitive to changes in temperature, while yielding max velocities and �tack driving� accuracy."

It sure works well in my 308 win.