If you're already looking at Ridleys, and want stiff, look at the Damocles, too. It'll be a bit stiffer than the Orion, with larger downtube and an oversize, tapered headset. The Damocles is probably also a bit more expensive. I know a couple of guys who race on Ridley Damocles bikes and love them.

And FWIW, you probably wouldn't notice much difference between your current 105 and a new Ultegra bike. IMO the new Ultegra is better, but I don't think the overall "feel" is significantly different from 105. And you seem to like the "feel" of SRAM.