Not quite the same gun, but the P99 I shoot in Production gets a steady diet of 125 gr Blue Bullets truncated cone bullets over 4.0 grains of VV N320. With the longer barrel of the Q5, you could probably get the same velocity with a tenth or two less powder. The reason nobody in Open shoots 147 gr bullets is that in order to get the velocity they need to make major power factor, they stuff a LOT of powder in the case, and with a 147, there wouldn't be room. Lots of people say that the recoil impulse is softer with 147 grain bullets. Personally, I shoot 125s because I like the way they feel better than 115s and they're significantly cheaper than 147s. Try both weights (as well as 135s) and see what your personal preference is.