Armatus(TT), Fire eel, Favrus(TT), wasn't aware python got overly large ( largest I've seen a picture of was about 18" and a few years old), but I'd put good money Uni-color gets fairly large ( they are built very similarly to TT's and M. Dayi), I have an M. dayi thats pushing 24".... and then a large % imo will hit the 12"-18"+ mark in captivity if you feed them more then just frozen bloodworms, and take care of them. Macro's ime seem to stay in the 12"- range.
If you want something big and will hold it's own an Armatus or favrus is what I would go with.. if you want a gentle giant fire eel imo is the way to go. If you don't mind spending some $$$ Uni-color would be a good way to look and if you like the TT's but want somethign abit different the M. dayii is very similar to them personality/aggression wise.
BUt to answer your question more straight forward, I'm not aware of any species that gets larger then Armatus or the Fire. or even comes close to hitting 3' let alone 40"+
I do however believe alot of the "max" sizes for this species group need to be re-worked. and alot of them simply aren't kept commonly enough to get solid captive sizes nailed down.
