I have 3 R9 280x running 1180/1500 +20 powertune and get 390h/s on two and 440h/s on the other on CN Heavy.  JCE 33b5 didn't increase by much - maybe 5%.  But wow my RX cards are nearly 30% faster than 33b.  And JCE was already the fasted CN miner by far.  Some are pretty close in miner-reported hashrate, but at the pool JCE is 10-20% better than all others.  I'm using BETA blockchain drivers.  Still the fasted for me.