did some more investigation. It seems that getting a gps fix hits my performance of the first menu load, back to a couple of seconds. I tried using the demo 'vehicle' and it didn't take this hit. So something in the interaction with real GPS is having an impact beyond just the redrawing of the screen for updated location etc. I am wondering if my n810 with built in gps gives a different performance profile to an 800 with bluetooth gps.

I've tried to wrap my head around what goes on in the gpsd vehicle code and I think I understand it. looks reasonably sensible. the gpsd calls it's callback method with new data. And we only read/set it if it's changed since our last read. Then separately something else calls another callback which returns the last held value for which ever attribute it wants.
don't know why that would be any slower than what the demo vehicle does. unless just having the gpsd itself has a significant performance hit.

Think I might switch debug statements on to see if it shows up any odd patterns.

On a completely separate note, I've added some info to my blog page about setting up the blue 'route' line to be thin and on top of the road rather than fat and underneath it. The wiki does allude to this option and I figured someone might be interested: http://danielwould.wordpress.com/navit-stuff/
I thought about updating the wiki with this information, just to highlight it, but I'm not sure where it would really sit.