I have the SLs running at ~500RPM. I can't detect any wobble, and they are very quiet.
These are the ones I am running (4 in my current p180 build):
http://www.performance-pcs.com/catal...oducts_id=4581
They do tend to vibrate a bit more than the S-Flex fans I'm running (probably due to the thinner frame-- the S-Flex frame is a BEAST), and they do have the slightest whisper of bearing noise. My fans are all soft-mounted, so vibration isn't much of an issue. If the vibration is what's killing you, there are some cheap-ish ways to soft-mount your fans, and wire fan grills usually kill most perceptible frame flex.
My only real gripe with Yates is their tendency to pick up fine dust in the bearings-- our family PC shares a room with a ferret. :)