I think 105 calipers are pretty crappy. I often encounter a stoplight at the bottom of a very steep hill---one where I need to stop while still on a steep grade usually and that's bad enough that I have to be extra careful about cleat/shoe slippage. I brake early and often, and my hands still hurt by the time I get stopped there. I brake from the hoods for a more stable dismount. My reach to the brakes is fine. I couldn't imagine going with calipers even worse than 105. Every time I hit that hill and have to stop (nearly every training ride) I wish I had at least Ultegra calipers.

That said, unless you were really bombing down the hill and hit the brakes too late, you still should've been able to stop with your setup, even though it may have been hard. This makes me inclined to agree with those that say you ought to reevaluate your reach to the levers from the hoods and how tight the brakes are. This doesn't mean your brakes are too loose. In fact, I feel I get better braking with slightly loose brakes, because I can really grab the lever tightly instead of only getting it to depress a little bit before the pads make contact--I can apply more force that way. You can get short reach 105 hoods (kind of a waste) or you can just put wedges into the hoods so that the brakes are closer to you. Being sure the hoods are positioned well on the bars for you, that the bars are rotated where the reach is comfortable in both hoods and drops, and also having bars designed for smaller hands will go a long way towards giving you braking stability without changing the levers up at all. If all that is ok, go with better calipers and pads for sure.