What I'm looking for in the N900 is:

• the "peripherals" of the N800 (SD card size, radio chip, no GPS, no slider)
• the form factor of the N810 (same size - or smaller!, faceplate camera, transflective screen and light sensor)

and fully differing from the N8x0 series in:

• a processor bump to the 3000 series
• RDS support in the FM chip
• N support for wireless
• Screen bandwidth limitation lifted
• 3D accel support