If you aren't going to use SLI, why do you need 3 x 9800GTX? What are you using the cards for? Do you already have them?
If you are just hoping to drive a bunch of monitors, you could get much cheaper cards that would save you a lot on power and still do all the normal things you need.
If you are gaming, I'd think you'd be better off with one higher end card (and possibly the others being lower end that drive the other screens.
Please give more information as to what you are looking to do and we can probably be more help.
Do you already have them? Have the cards.
What are you using the cards for? Cooperative computing. Seti, Collatz Conjecture for example.(See Sig link).
Not driving Monitors.
The question as asked is valid.