I have been using phoenix under aoclbf and never had any stale/reject problems on any of the pools.
On Ars have 0.7% (my backup pool)
edit: I see i'm getting between 6-8% stales now on your pool
Stale will be dropping in the coming shares, overall pool stalerate across all miners is at 1.4% atm so its just a couple of miners it seems with either broken miners or just not efficient miners, I dont know at this time.
You could either wait and see if your stales drop and you should be fine or try cgminer/fixed poclbm or diablominer (whichever is fastest for you) and see if your stalerate improves, I would think its worth the little extra effort for the payouts we make

Btw farfiman your most recent stats on our database since start of new payment cycle shows 3.1% stales, its clearly dropping just keep an eye on it. If everyones miners is working right, they should all move to the pool average stalerate thats at 1.4% right now, eventually when shares catch up.