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I know its been done before but still a bit confused after searching.

The situation:- Previously using an old battered set of Mares X3 fins with beaver spring straps.
The new seaskin suit has a size 10 boot but its also a 5mm neoprene boot so a large foot. The foot no longer fits into the old fins,i get cramp surface swimming plus in forcing it i've stretched the spring straps so much they aren't tight on my wet boots now.

So, time to buy a new set of fins for the drysuit. I've tried jets before and liked them so want some. The problem as ever seems to be sizing.

Can anyone offer a guess as to what a size 10 with 5mm neo boot would be in Jets (XXL too big?) or would i be better trying turtles (if so what size?).
Also, what sort of size spring straps for those (non beaver).

My first intention was to try them on in LIDs (even took my suit) but failed to find anyone selling Jets and only 1 place with turtles and then only limited sizes so im going to have to buy blind on the internet - not ideal but i really need a set to fit me on my new suit. I don't know of any dealer local to me to go try either either.