No, it's not a "toned down" version of the 6800, it's just a 6800, plain and simple. Anandtech did a nice value/perfomance
review on some of the newest shit, and I found it quite helpful in my quest for knowledge concerning the issue.
Tom's Hardware can also be helpful in finding answers to your questions.
In any case, back to answering your question. Nvidia has priced out the 6800 at around 300 bucks, and vendors are pricing it around that point, so seeing a "regular" 6800 on newegg for that price is of no surprise. The other 6800s that I assume you refer to, the 6800 GT ($400 USD), 6800 Ultra($500 USD), and 6800 Ultra Extreme ($540 USD, not entirely sure at this point) all rank higher and higher on the performance scale, in that order. To answer your other question, I would expect about a 50% performance increase against a 9800 Pro, but nothing beyond that. Hell, it might be below that. But, I say to you with no ego that the 6800 Ultra literally brings about a 300% increase in power (according to Tom's Hardware's 3dMark2003 test scores) to the table. It's the first real jump in performance that the industry has seen in a while.
Now, with that info under your belt, you have to consider, is a 50% performance increase really, really worth the extra 93 bucks? I mean, seriously. I made the same decision when I bought my card (ATI 9700 Pro, 2002), and I saw about a 50% increase against the GeForce 4 Ti4600 in all tests. I didn't consider that at the time, but that's, in reality, exactly what I payed 280 bucks for. Mind you, this was a serious upgrade for me (all the way up from a GeForce2 MX440), but I was still only getting a 50% performance increase when compared to the previous generation.