Optimun nvidia non-gamer configuration

I would swap the 8800GT as the primary and run the two 19" of the GF9500GT, since hen playing games (which you don't do much) or doing anything stressful (which you may do more) it will go to your primary card for acceleration. Since the two 19" monitors live mainly in a 2D exntended desktop role, the GF9500 would be more than enough for them.

No benefit to moving to another GF9500GT at all, not even for the potential of SLi'ing them (the GF8800GT would probably still outperform them in that scenario).

Is there a major issue with your current setup though? As much as I would put the GF8800 as the primary, in this mainly 2D environment I doubt it would matter. Only if you were crunching some serious calculations (be they 3D or GPGPU) would I bother changing your configuration just because one would be 'cleaner' from a setup perspective.

You would see minor performance differences in Vista due to the vector nature of the desktop, but even then you reach diminishing returns on the power of your graphics chip so I doubt it would matter much, and if anything once again your primary (most active and stuff-filled) monitor would demand the most. Win7, dunno, it's so beta right now, that it's like Vista before they crippled it for intel, I wouldn't hazard a guess until we see final code, because you couldn't tell if lag was, kernel issues, hardware issues, immature driver issues or else just transient bugs somewhere else in the system (memory management, etc).

As for digital versus analogue, not much difference, mainly it depends on the situation. For medium size lengths with limited shielding, digital is better, for longer throws analogue is better; for properly shielded cables or short lengths both are very equal in their quality.

The time you will want to change is if you get a panel that has higher bit colour depth which is only supported via DVI/HDMI/Displayport, but that's either and HDR LCD or some other 10+ bit (source supporting, not internal) panel. Or of course if you MUST deal with HDCP content and thus require the digital handshake.

For what you have now, no worries, go with what works for your setup.