I thought it was the geometry of the RD that determined max cog size. The cage length only determines chain wrap capacity. To use a cassette with a 32-tooth cog, I would think using the Rival or Apex derailleur would be the only options, swapping the cage on another model would not change the max cog size for that model.
I'd be happy to be corrected on this if someone knows better.
firstly hi im very new here, so i hope i dont step on anyones toes with my post but just my 2cents worth if your interested.
yeah from what I understand this is correct. The only reason that you would go a longer cage is if you decide to run a triple crank. As there is a greater difference between the smallest and largest chainring, as compared to a double crank (compact or standard). Hence the need for the longer cage to be able to cope with chain tension.
It is the derailleur body itself that determines the distance from the largest cog on the back to the top of the "guide" jockey wheel. So thats why swapping the cage, unfortunately won't fix your problem.
If you want to run sram and be able to have a 32 cog on the back you will need to use something like the apex. But as you want something a little more high end I would go the xx derailleur. Just like fairwheel have done. Even David Miller used one in the Giro Mountains.
yeh i know he ran a 36t but there is no reason why you couldn't run a 32t cog