The only con is the price, although I think the Xylotex is not powerful enough to use the 5 start.
Also, 1/2-8 2 start is quite a bit cheaper than 1/2-10 2 start. About $20 cheaper for a 6' screw.
5/8 has more inertia, so it may hurt your accel a little. And I use Dumpster nuts, which you can't get in 5/8".