As far as the qualification for IPSC part, there is a 5 page thread on the Brian Enos forum that goes into quite a bit of detail on the various rule books.
I prefer the X5 due to the 5 inch bull barrel(4.7 inch standard profile barrel on VTAC), as well as the fact that the X5 is Romeo1 optic compatible, and has the extended slide catch lever(reduced slide catch lever on VTAC).