I'll be going with the 5.13 as well. If I ever upgrade to 40's, which I seriously doubt now, I think that 5.13 and an PR60 in the front would still work fine.
With a set of 40's, 5.38 is really the ratio that you want but yes, 5.13's will work fine too.
I know that you run Rubi-Cat with a PR44 front and an PR60 rear and you are happy, right?
Yes, that's what I'm running now only I am now running 5.38 gears. Having run it and 5.13's with 37's in the past, I can tell you that for me personally, I wish I still was running 5.13's. Again, for me, 5.13's are a better match. While I am running our old 40's on Rubicat right now, it was more for brake testing than anything and I will be dropping back down to 37's as soon as I get my hands on some new tires.