Don't know much about the RS120, but that is still a pretty good deal on the X1. Only real cons at that price range for those headphones is a slightly recessed midrange and some might find the bass too much.
Very good soundstage with a slightly V shaped sound signature, which would be awesome for gaming. V shaped as in, sightly forward bass and treble, with recessed mids.
EDIT: Keep in mind though that the X2 is out and was an improvement in almost every way. They were on sale today for $230, but amazon had a regular sale on them for $250 a few months back. Another headphone to look at in that $170 price range is the Sennheiser HD598. In my opinion a lot more balanced sound signature compared to the X1, while still being more "lively" than a purely analytical headphone. Note: that these both are open designed headphones, so sound will leak in, and out.