Dell U2715H and U2713HM Dual Monitor Setup

Hi Guys,

I have a Dell U2715H and a U2713HM. I am planning to have a dual monitor setup. My current graphics card is an old GT610, which only has DVI, VGA and HDMI out.

I've connected 2715 via HDMI and 2713 via DVI, however 2715 gives a less bright, less natural image at same settings as 2713 which is on DVI.

Current graphics card doesnt have DP output.

I am weighing options,
1. Replace 2713 with another 2715 and upgrade graphics to one with dual DP output
2. Just upgrade graphics to one with DVI and DP output.

I dont do any hardcore gaming, or graphic intense activities. I mainly use work documents, to have multiple windows open at the same time, watch youtube videos and occasional photo editing.

Something comfortable to work few hours at a time would be great as I wear glassess.

I am not very uptodate with latest tech stuff, so any advise is appreciated.

Thank you