Using a 3.2GHz PC with WinXP+SP2, SX 3.1.1 and TI bits 106r2, I seem to getting very stable arps today (might be down to the phase of the moon or something...
).
Actually I have a whole stack of parts outgoing via midi as I write - 2 drum tracks with a motif es, an arp running on a v-synth and an arp running on the TI (in Virus Control with its USB audio return) a bunch of audio parts I recorded earlier, reason 304 loaded and playing some parts and the resulting mix going to my 01x which is also dealing with the audio coming back from the other synths.
For once the whole lot seems to be in perfect sync at 140 bpm and no glitches either with quite alot of audio and midi parts going in and out
I am now in the habit of rebooting my PC before I run my audio applications - seems to hugely improve stablity and accuracy. Maybe worth doing the same if you have an apple as well.