Rico has finally posted some numbers that show you the performance he's seeing with Beta 2 bits (sorry you don't have yours yet, we're working on it.)
A compiled query executing at about 93% efficiency (that's only 7% overhead over raw SqlDataReader.)
I know, I know. I still don't believe it either and I wrote the code!
And that's under explicitly biased conditions to try to magnify the overhead as much as possible. You are almost never going to see this much bias in the wild. That means that using compiled queries will most often reduce the overhead to approximately zero. That's right. I said 'zero.'
And what if you don't use compiled queries? As it turns out, we got a lot better there too. Rico's tests shows his query executing at about 1.8x, (that's about 80% overhead over SqlDataReader.) To tell you the truth, I still don't like that number so I'm going to be working on it some more. :-)
As it turns out most of our lab performance tests don't run in as ideal of conditions as Rico's setup, trying to model more real-world conditions to base our goals on. In those tests, with the database sitting on another box (still dedicated & high-bandwidth), we tend to get numbers more like 1.3x (30% overhead.) Of course, YMMV, since there are so many dials to turn to change operating conditions, etc.
So are you 'chomping at the bit' to download Beta 2? You should be.