Reading through the book Mark of the Xenos, I at first believed the weapon damage to be in line with the generally reduced figures in the errata. I noticed that the Kroot Shaper's pulse rifle on p. 20 uses the 1d10+12 figure, but only later saw that only 10 pages further the pathfinder's pulse carbine does 2d10+2 damage. In addition, just about all the Chaos Space Marines presented in the book use the older, larger numbers for their weapons. I can change those pretty easily to use the new numbers, but if Tau weapons are intended to compete with the old figures it seems like my players would always be outmatched at range.

Well since the eratta has the Tau weapons in it with a Pulse Carbine at 1d10+12 I'd say use that... but generaly you should be somewhat outmatched at range vs the tau. it's prety much the only thing they have going for them.