The final output of the content I am creating is 5.4k x 2.7k resolution at 60 fps. The composition consists of two to four 4k 30 fps video files, 5.4k x 2.7k still images, a good amount of filters and effects like keylight, key cleaner, and advance spill suppressor, and is frame interpolated from 30 to 60 fps. Render time on my rig (i7-5820k, 32GB memory, 970 GTX) is about 3.5 to 4 hours for one minute of footage. A bulk of the render time is caused by frame interpolation, which is absolutely necessary for what I'm doing.
To speed up my render times I was considering either building a new rig (budget $2500) to use in conjunction with my old rig and BG Renderer. or buy 5-6 used Xeon E5-1620/E5-1650 workstations to use with aerender. I figured the E5-1620 workstations would be the best route since it has a higher clock speed and single core performance than the 1650. Would I need to install a dedicated graphics card on the workstations?