Need Advise for GPU - 2560X1440 - non gaming

I have a 4 year old set up I want to take to work. Primarily going to be using it for Word, Excel, couple work programs and surfing the internet, youtube, streaming music and hd movies e.t.c...

I just ordered a 25" 2560x1440 16:9 Asus monitor and looking for a graphics card to maximize the resolution the monitor is capable of.

Rig is as follows
Gigabyte Z68X-UD3H-B3
i5 - second generation
16 gigs / corsair vengeance ddr3
650w power supply

Currently have a MSI 560 ti installed with 2 DVI Ports

Debated on just using above video card and getting a DVI to HDMI conversion cable. Looking at MSI specs it says 2560x1440 is max resolution card can do. Am I better just using this card for general use?

Looking to get something that has HDMI or Display Port. Have been looking from 750 ti up to 960 gtx and am not sure if this will be enough? or overkill for a general use computer at 2560x1440.

Would the newer video card give a better video from the same source? Or would I only notice improvement if I was only gaming.

Thanks for reading my rambling. Any and all advise is welcome.

A 750Ti is more than enough for general usage. Honestly the 560Ti should be plenty too, I would try your system as-is first.

I would just purchase the DVI to HDMI conversion cable, those cards are for gaming and work.