Can Sonar buffers be too big - lead to funny behavior?

Very large ASIO buffer settings will require larger disk I/O buffers to match if you have a lot of audio tracks being streamed. Otherwise it should not really be a problem. I like to keep the SONAR performance meters under about 40%. I don't do much of anything that requires a buffer over 512 samples to achieve that, but I'm not a power user when it comes to synths and FX.
 
For bouncing/exporting you can enter a non-zero value for BounceBufSizeMsec in AUD.INI that will be used for offline rendering (zero tells SONAR to use the ASIO buffer size for offline rendering as well). In theory this can help speed up offline rendering, but I haven't ever seen a significant effect. I have mine set at 20ms just to avoid problems rendering some synths with ASIO buffer settings under 4ms.