sounds about right.  the Quadro FX 5600 uses the G80 core and is essentially the same as the 8800 ultra.

my 8800GTS 640MB (same basic G80 core) pushes about 18.5Mhash (using the below settings) and has 3/4s the number of stream processors (96 vs. 128) and 5/6ths the clock speed (513MHz vs. 600), so if things scaled exactly, you would get about 25.96, and you're getting a little faster than that.

might try playing with the extra parameters.  i get slightly (about 0.5 Mhash for me) better results using -w 128  than whatever it defaults to.  -f0 will also squeeze a little (about 0.3 Mhash for me) more out of it, though at the price of slowing everything else to a crawl.

don't even think about using -v though, it slows it down massively to about 13Mhash.

just try poking different values into -w and see what happens.