Interesting post Sardonyx. I have just bought a 700, for about the same reason. I find the Yamaha Vocal Harmony pales compared to that of the Korg's versions. For the price difference, I managed to buy the TC Helicon device along with the 700 and STILL saved $300 over the 900. I Use a Korg PA 600 as the lower of my 2 keyboard setup along with a PSR 970 (which will be a home keyboard from now on ) along with a Digitech Voice 5, which will be retired! I am essentially a live performer, (vocals and keys) and the Yamahas are way better in finding song files in a live situation. The keybed feels better on the 700 and the build seems better. I travel the world with my keys (I work the Asian market and also Spain), and the 970 hasn't stood up to travel as my old PSR 3000s, with cracks appearing on the casing and a couple of keys are becoming 'iffy'. .
I reckon I'll retire in 3 years time, and (hopefully) this will be the last keyboard I will need.