1. the color space of your display should cover as much of 9900 color space, as possible. You may expect, that the more aRGB it covers - the better, but it's not that simple
2. SVII is an excellent profiler, and it allows to utilize the whole potencial of NEC x90/P221W. I use i1pro to calibrate NEC panels and it works like a charm
3. i1pro is supported by SVII so yes it'll calibrate the NECs
4. You may also consider NEC 2490WUXi, but it's not a wide gamut panel (neither is the Apple 24")
5. 2690WUXi is larger, has higher resolution, higher bit (12) LUT, electronic uniformity compensation and H-IPS A-TW panel with slightly wider gamut. P221W has only 10 bit LUT, no uniformity compensation and S-PVA panel - in practice it doesn't calibrate as good as x90 NEC series panels.