I personally use xScope almost exclusively. It's the best combination of simplicity, speed, and features that I've found. I think the implementation was fantastic on almost all accounts, except for bookmarks, which could use some improvement. I also did some speed tests of my own...it went like this from slowest to fastest.
Slowest to fastest browsers based on my tests:
Skyfire
gap
Dolphin HD
gap
Stock/xScope (essentially tied; stock ever so slightly faster)
gap
Opera mini (destroys all in speed, but not all pages render correctly)
Opera mini is the way to go if all you care about is speed, but not all pages render in the way you would think since it has a server processing it and compresses it in a certain manner, so flash/images/layout, etc. might be messed up. Stock and xScope were essentially a wash in performance, but I liked the additional features xScope had. It's super simple, but has all the necessary components like tabbing, favorites, multi-touch zoom, the one finger zoom, "smart" zoom, clicking links, copy and pasting text, searching text, history, custom skins, auto-hiding toolbars, and more.
The stock browser isn't too shabby in my opinion either, but xScope offers a few more functionalities without compromising performance. I use skyfire for watching videos sometimes as it works better. I have Dolphin HD installed, but really haven't used it at all. Seems almost too "feature-rich" and messy. I want a simple interface that has the functionality I want and good performance. I agree with the OP and xScope has been the best browser based on what I look for.