Excellent description of the river. Make sure to scroll down to see the pictures:
Good description and advice on maximum flow rate for kayaks/canoes:
Paddling Tips: There is only one short rapid (Russian rapid) just below Knights Ferry. Inadvisable in an open boat above 500 cfs, all canoes get swamped above 800cfs. This is a blind rapid with a well-marked short portage trail river left. The trail can be paddled at 1100cfs.
This is the only picture of Russian Rapid I could find:
This California Water Department site has river flow info for Stanislaus River, measured at the release point at Goodwin Dam. Use the Spill cfs for reference:
Here is a discussion about high flow leveals in this section of the river:
Inflatable Kayak Report