I have two Whispers and a Whisper/300 BLK, For a supersonic load, I like the Nosler 125 gr BT using either H-110 or 296. For a sub-sonic load, I've been playing with the Sierra 190gr MK with AA-9 or AA-1680 but haven't settled on a final load yet. The supersonic loads, I'm loading in reformed Remington .221 FB cases. The sub-sonic loads in Remington 300 BLK cases. Primers are Fed 205M's.
2400 is another powder that works well in sub-sonic heavy bullet loads. In supersonic loads, 2400 won't develop the velocity that H-110/296 will.