I have two 2560 x 1600 monitors.
I have run them both on a XFX 7600gs which had two dual link dvi outputs., and one on a 3450. It does not take much to run such a monitor when used for relatively static stuff like e-mail and browsing web pages.
Gaming is another thing entirely.
Something like a GeForce 210 should do the job.
Since you already have the quadro, it should run ok on a 350w psu. It is only the cards that need an aux 6 pin pci-e power connector that need more than 300 watts.