Yeah, I was getting massive crackling, crashing, pitch bend spikes, radical oscillator drift, and unresponsive keyboard with 5.0, just like I did with 4.5.3 so I've gone back to using my external audio interface. Crackling gone, no crashes, no oscillator drift, no spikes, keyboard is responsive. Sure would be nice to use the VST, but for me it is totally unusable.
Model Name: iMac
Model Identifier: iMac9,1
Processor Name: Intel Core 2 Duo
Processor Speed: 2.66 GHz
Number Of Processors: 1
Total Number Of Cores: 2
L2 Cache: 6 MB
Memory: 4 GB