I like 525 and 550 rio heads (rio iflight in the 550, rio flight 525 and a skagit short by rio in 550). It handles a 600 iFight as well, but i felt like that line was just heavy enough to take the crispness out of the rod. I was told the rod was designed for a 540 skagit. I did not like the shorter Skagit short heads as much as I do the Skagit flight. Lost my skagit short 525, and did no replace it.
Funny I just did something like this this week. It was a 525 flight with a 15' clear head from 7/8/9 DT Spey line (line is long gone, tips are around). I had 3' of fluorocarbon leader, small cone head tube and felt like a Ninja. Threw it like it was nuttin'.