The new X2 rack gear sounds fantastic, but touring pros have problems at music festivals and locations with multiple wireless devices in use. I was talking with one pro's tech (sworn to secrecy but someone big) before a show... when the X2 stuff is in a smaller venue he loves it, but he keeps the guy's older Shure ULX system in the rack for times when the airwaves get busy...
I swear by the Shure SLX system, but also love the X2. Some links you might find useful:
1. Our in-depth look at the white space and 900 MHz issue... if you're considering buying used gear then definitely read this first!
http://www.musicplayers.com/features/general/2010/0610_700MHz.php
2. Review of the SLX wireless system:
http://www.musicplayers.com/reviews/guitars/2006/0406_ShureSLX.php