With a 6800NU you'll probably have to unlock the extra pipes and OC a little to 370/1000 or so to get the same performance. I havn't tried with OGL2 yet, but with 1.5 I could get the same (or pretty dang close) results out of my 6800GT OC (stock 4000 runs at 375 core, 6800GTOC at 370) with the
SoftQuadro mod. The other features aren't so much locked as not used by the drivers. I don't know if any revisions have been made to the chip since then, but mine and other people with older 6800's get the same results.