I haven't owned IROKS, but I wheel w/ lots of people that have them.
I LOVE my Rockers in the snow... I think in the snow, Rockers are better... but it is always hard to tell as the rigs I wheel w/ are all setup a little different, and IROKS do very well in the snow too... way better than an SX or TSL.
In all other conditions, I think they are comparable... but from what I have seen, and what I have read on Pirate the Rockers will last WAY longer than an IROK.
I should also add that I did a little grooving on my Rockers before I ever put them on when they were brand new... maybe this helped them out??? Beats me?
Also, some people have problems at really low PSI w/ Rockers and beads. Mine are on H1's, so I don't have any opinion or issues with that.
This is how I grooved mine.