OK, this is an approximation (for "last interval" values) of the (live) sniffer after a couple of hours' running:
Max Interval (ns) Max Jitter (ns) Last Interval (ns)
Servo thread (1.0ms) 1003059 7899 995609
Base thread (25.0us) 41894 16928 24937
This is, of course, with "isolcpus=1" (per 07_rtai), hyperthreading off in the BIOS, and a number of pdfs (including a coule of the larger LinuxCNC manuals), Firefox (a few tabs), "Eye of Gnome 2.23" with the original (and only) screenshot loaded, Synaptic packet manager, Ayam (NURBS modeller), the system monitor, the sniffer of course, a folder window, glxgears, and three terminals (one of which glxgrears is running from as "glxgears &"). The machine is also connected to a VPN session on the iMac as well (it looks much nicer on the iMac's sharper screen than on the rather iffy touchscreen, and is about the same size).
Note that the "Max Jitter" values haven't changed in those two hours. Also note that the system monitor shows the single operating CPU as being max-ed out at 100 %, the other one is sitting idle at 0 % (of course).
This is on the first system that I installed; 12.4 % of memory (out of 4 GB) used, and o % of swap space used. The CPU heat sink feels "mildly warm", but it also has a 90 mm fan (connected to the D525's three-pin chassis fan socket) blowing across one end of it (the mess of cables on the desk has pushed it out of way of the bulk of the sink).
Interestingly, the network part of the monitor is showing sustained high ethernet activity, due to the VPN link with the iMac, no doubt.