I have two 700c Dura-Ace equipped bikes, and a Pocket Rocket Pro with 105. The performance of the 105 gruppo is definitely not as crisp for two big (and probably several less significant) reasons:
1) 105 simply isn't as good.
2) Because I travel with the Bike Friday and am folding/unfolding on a regular basis, the cables get stretched out, and I find that I need to make minor adjustments fairly frequently.
Obviously, #2 is going to be a big factor for you, and I suspect the Sora gruppo will be a similar step-down for you from your Ultegra gruppo. Just be aware that even if you find that Sora works for you on a non-folder, that you'll have a slight decrease in peformance based on the folding/unfolding and its effects on the cables.