What I have noticed is subtle, I have xruns in both situations but the rate increases noticeably. I've been running patched kernels but there are all kinds of parameters (as I'm sure you know) to tweak before it is sufficiently solid. I would consider my findings pretty much expected behaviour with a less then perfectly tuned system. The real problem is that it's so very very hard to tune a system sufficiently without hours and hours of work. It would be very nice if there was some way to automate, atleast parts of, the process.