I have not yet eliminated the possibility of the 588, either. It's a 500 with 88 hammer action keys. It looks ugly but sounds great. (in my not-so-humble opinion).
However I struggled with the key action when trying to play non-piano type voices especially those with velocity-controlled effects like the slide guitars. Even after setting the sensitvity at it's lowest, I had to really hit the keys hard to produce the slide effect. I will give it another try before deciding - it's a great buy right now with Korg's $400 rebate which ends next month.
Tim