There more graphic you wish to send the more bandwith is needed.
I am running a GIS application, that are using lots of graphic. I got 10 user on a 1MBit line, and it works fine, absolute no trouble.
I am also running a SAP client over GPRS. The bandwith is 18-24 kb. It has been difficult to set that up, so it works. But it works. The SAP Clint has only gray color and are not showing any graphic.
So you have to fins out, how many users are on the line. How big is the bandwith, and what type of program are you gonna send.
Then set up a test with, that will be a min scale of your real setup.
But Citrix is a thin client. Doubt that you find anything thinner.