I'd be surprised if there wasn't a 64Gb version for the iP5. I ended up with a 16Gb iP4, as I would have had to wait months for the 32Gb to be restocked when I bought mine, and at first I thought it was way too small and I was running with about 1Gb spare. Over time though I've got rid of more and more stuff off it, apps that I never use or music I hate now, and also started emptying the camera roll once I've backed it up on my PC.
Don't get me wrong I'll still go for the model with the largest capacity on my next upgrade, but I highly doubt I'll actually need it all.