The machine is an Intel P4 3.2Ghz with 4Gb memory, /3Gb switch, two hard disks. While "idle" (i.e not playing anything) the FXT server (server.exe) sits at around 8% CPU, and ViennaEnsemble.exe fluctuates between 20% and 25% (according to Task Manager).
I have another machine, pretty much the same spec, also using FXT, but with GVI. On that machine server.exe runs at about 8% when idle, but that's it. GVI seems to only use CPU when it's actually doing something!
As I said, I was just curious. I was just surprised to see 30% CPU even when it was doing nothing at all - it's been totally silent for hours and 30% CPU throughout! But it all works well.