I have never seen any dyno sheets on just a LS/VTEC so I can't remark on the gains but if you want to go this route you need to rebuild the bottom end to handle the higher revving of the VTEC. I would say go for it I have heard good things about it also and if you can do the work yourself you can save a lot of money. The gains would really be dependent on the parts that you would use for the build.