Never put all your eggs in one basket...it's a bad idea. Go with 2 smaller cards.
I also purposefully use smaller cards so that I have to change cards more often. I hate to have too many images on a single card....makes me nervous.
This line of thinking belongs to another era. Some cards and particularly the dreaded Microdrives used to deliver dubious reliability. But that's way in the past. Back when CF cards hit a massive 1Gb, the Nervous Nellies freaked saying they'd much prefer the safety of four 256Mb cards. When 8Gb cards started shipping the Nervous Nellies were out again saying they'd much prefer eight 1Gb cards...it's safer. And so on. Shooting daily onto CF since 2001 I've never lost a card to corruption or damage. I routinely retire them every couple of years and get the latest...
I no longer buy anything smaller than 64GB. I have a CF and a SD that I use in my 5D MK III. I do use a 16GB card in my old 40D. That way, I can shoot a entire evenings worth of images plus a few short video clips without worrying about card space. I typically use about 40Gb...
...and like Mt Spokane, I no longer buy anything smaller than 64Gb. Next year that might read smaller than 128Gb.
So gshocked, I'd just get the biggest high quality card you can afford. Personally I'd be nervous about missing an important shot because my tiny card was full, not to mention the avoidable logistics of managing of a pocketful of filled-up cards AND the increased potential of over-writing a card you haven't yet downloaded.
Come to think of it, gimme the 128Gb.