General consensus amongst those that have had to endure the problems with the rest of the ranges the SU73s are underpowered, the I5 range is the one to go for. However then you need to really get the maximum spec GPU. Even then you need to purchase the R2 variant as it doesn't have problems with the hinge, like the earlier R1 variant. Then you need to make sure its NOT a refurb as many of them are, the difference seems to be that the keyboard is notably UNLIT and the keyboard is often US with Transfers to change the keys. In addition to that there has been some problems with the Drivers for the various GPUs as they're 'Dell Versions' which means as of a couple of weeks ago where as Nvida\ATI has upgraded their drivers for their cards, Dell were a generation behind and everyone was waiting for them to catchup, it was then 6 weeks and despite numerous emails Dell was somewhat quiet on the situation.
HTH