OK, all you helpful people, new question: I have the I/O buffer set to 256, and this seems to work without creating any latency problems. Any reason I should try a lower setting?

If you're happy with the latency at 256 then go for it! But the lower the I/O setting the lower the latency :) It's good to become comfortable changing the value when recording and when Mixing to ensure you get the best performance. I usually keep my I/O setting around 128 when recording - or I turn Software Monitoring off and use direct monitoring through my audio interface... and when recording it's often at 512 or 1024...

So you find that 128 doesn't stress the CPU too much when recording, even if you have a lot of tracks and FX in a project?

huh... you didn't mention effects ;-)) But seriously, sometimes it does. It depends on your workflow... I might record and arrange and mix somewhat simultaneously... other times, recording takes precedence and then I'll be mixing and adding effects later down the line. The I/O Buffer size you can use would vary, as you mention, per project and per system. I know many users who are on an I/O setting of 64... Have you tried enabling the Low Latency Mode? (Should be in the Transport...) It will limit the latency caused by plugins and bypass plugins that are causing too large a delay. Also, worth bearing in mind to steer clear (if possible) of latency inducing plugins, like Reverbs, delays, limiters... But with Low Latency Mode turned on you should be good to go! Thanks Rounik