I know bigger is better in most things, how big is the MINIMUM bandwidth that is acceptable for use with a small installation on 3CX? Is 512K upload acceptable? 750K?
It all depends on how many concurrent calls you have and then the codec you'd like to use. 100K per call using g711 is the usual budget, add some for overhead but make sure that if you use that line for browsing as well that you have a QOS enabled router