I'm not sure that the Obutto would be 'worth' £350 more, wouldn't it be an option to buy the keyboard tray separately (I think it's about £80ish) and see if it can be engineered into the GT Omega rig?
I use the Obutto and a friend has the GT Omega and I don't think either of us would change.
I do use mine for FPS stuff too and it's no problem, although I use the additional perspex tabletops for my keyboard though, and I have the keyboard tray as a big arm rest/mouse pad. Works well for me and never gives me issues.
Looking at both I think personally I'd still favour the Obutto, it seems more versatile and with the perspex tables etc will allow you more setups etc. On the right perspex table I have my button box mounted on the arm for instance.
Can provide a pic if it helps.