My hash rate is 380MHs on aggression 7 when no other application is running, when I start an Internet browser chrome or opera hashrate drops to 335~340MH/s, as soon as i close the browser it goes back to 380. (No FASTLOOP flag is set - it is ON by default)
In case of aggression 11 my hashrate is constant 355MH/s no mater other software running or not on the machine, no matter FASTLOOP flag...
what's your CPU usage like? have you tried a different version of phoenix? (although 1.5 should be fairly stable). you could try a completely separate miner, as well. do other applications make it slower, or is it just chrome?