The .400 cal 200 grain XTP is a great bullet for deer. I've taken 2 deer in 2 years with them- both boom-flops. Both shots were around 100 yards. As far as velocities go, I think that you would get the best performance with 80 - 110 grains 777 or equivalent. I'm not sure if I would use 150 grain magnum charge with this bullet - they can fragment some or get jacket separation at extreme velocities. I'm not a speed freak, so I use 80 grains 777 in a .45 cal. I'm not saying they are the absolute best bullet out there (I'd love to play around with some other rounds too), but I have about 35 bullets left of a 100 round box, and I'm happy enough to stick with the XTP's til I run out.