Personally, rather than use a commercial app, I went with Hylafax. I downloaded the latest beta3 (for Rh6) and installed it on E-Smith 4.0
I had to add a heap of packages first to satisfy dependencies (such as ghostscript, which required xfs and so on), but it was all pretty easy. (I knew I held onto those old RH6.2 CD's for something!)
One big thing, I had to d/l RPM4 to be able to install the Hylafax rpm.
Once installed, it went like a breeze... Until I tried to get sneaky and change my symbolic link that I created from /dev/fax -> ttyS0 to ttyS1. I, erm, put the target and the link the wrong way around... Killed my ttyS1. Bugger!
(Anyone with hints to get it back? Modprobe and SetSerial hasn't worked so far...)
As for performance? Great. You have a wide choice of delivery systems - by editing a simple script you can pipe it through GhostScript to print out on any printer (in my case the office photocopier @ 22ppm), or to email the TIFF (or a link) to a designated person in the office.
Oh yes, and you get clients for sending via the HylaFax too. And it's a free app.
Cheers,
Ant