I use the Rio 550 grain with the 0.34 40 lbs running line and a range of medium 10' MOW tips (made of T11 rather than T14). The maximum with 10' of T11 does get you down quite a long way. It's a very good set up on the Cult - which will cast anything - but you do have to slow things right down to preserve a good anchor. I used it for 2 days on the Findhorn last week in the worst of the weather and the highest water. The Rio solution is very good but more expensive than the other options, especially Airflo, but I have no experience of them: others may be able to help.
For cold and heavy spring water I prefer a full sinking shooting head with a very fast polyleader on the end.