If you want 350rwhp an you get the gcg high flow factor in doing your cams as well, I have searched on these forums and not that many high flows have reached your figure of 260 rwkw.
The GT30R will be able to achieve this figure easily with more tuning maybe more, I have had a good look into the two myself. Im going with the GT30 I guess it depends on a few other things though as well like wat are you wating to do with 350rwhp ,track ,drift ,1/4. Wat other supporting mods would be in place to back up the turbo.