Mike, at times I have had some problems with just about all split rings when putting them onto big trebles like a ST76 5/0 or Gamakatsu Recorder. Patience and gently goes it is definitely the way, but I am sure you know that.
I think the most likely to keep its 'spring' and shape is the Decoy split. I usually use the #9 and #10 (200 and 250 lbs). Owner hyper wire in #10 and #11 (220 and 250 lbs) are cheaper, but almost as good alternatives. Varivas I cannot say as I have never used them.