Starfish, your hands sound very similar in size to mine (though probably not as chubby--my mom *still* teases me for having chubby little kid hands). I think my middle finger is about 3.25" and my palm is about 3" at its longest line. If I were at home, I would measure it, but I'm currently trying to trick myself into being productive by sitting at a coffee shop with my laptop.

I do have one shim in my R700 levers, and I know I have the option of putting another in there, but I don't need it. Unfortunately, I can't compare my levers with the 105's that you're using. I went from the un-adjustable Tiagra levers to these.

Here's a link to the levers I have on the Shimano site. If you're ever near Seattle, let me know and I'd be happy to let you check out the levers on my bike for yourself. Even on eBay, they weren't exactly cheap, so I can understand the hesitancy to drop money on something that may not meet your needs.