Any question answered...

You could get a new 105 chainset and rings for £90 ?

You'd be paying £90 simply to get hollow crank arms. Which you won't notice.

Problem I've got is, the 2 rings do cost about 80 combined which is fine*. That's comfortably affordable for a worthwhile and pretty big upgrade from the r565 crankset I bought from eBay for £45 new. The whole new crankset for just over £121 is stretching the budget quite a bit though but its a completely new chainset... Arrghh

The only reason to go Ultegra rings is if the shifting is sub par on the standard 565 rings. No?