with apologies for continuing on this thread - this is really just for reference if anyone else has the same problem with the trangia x2 multi fuel burner.
After the 37 jet I tried 45, the same as the omnifuel. It works even better than the 37. I emphasise this is only my experience on my x2, everyone else seems to be ok using the 32 jet. It simmers better, and is a much more stable flame, even with a gas canister with only 10% gas left.
If I was buying one again, i'd ask for a store demo to check it worked ok with cylinder gas before leaving the store and parting with money.