At that resolution, Cf 4830s would be fully CPU bound and a waste of $$.
Any single 48x0 will be more than enough for your.
Even a 4670 will treat you nicely at that low of a resolution.
I would recommend purchasing a 48x0, another 2-4Gb of RAM and starting saving up for a new monitor.
With a single 48x0 now, you will have the option to Cf later if you decide it is necessary on a new monitor.