There have been a few re-installs of FSX along the way and various tweeks and the odd utility here and there, and a few headaches as well. I went through a phase of 5 second pauses, low frame rates, BSOD nv4_disp.dll crashes and some hungapp crashes. They were driving me to distraction

Well , I used to use BitDefender which was OK, it had a gaming mode, but a few weeks ago my subscription ran out. While I was re-installing everything, I came across a free copy of Norton on my Gigabyte drivers disk, so I thought why not? All the problems above ceased when I got rid of Norton and installed Microsoft Security Essentials. Now running smoothly with everything pretty much maxed out, full WOAI install running at 70% traffic load (any more than this and you get horrendous queues at the holding point and more go-arounds than you can shake a stick at).
I'm getting 15+ fps at UK2000 Gatwick Extreme v3 on the Go Extreme! configuration and 30fps at stock airports (set to unlimited in the sim but with a 30fps limit set in nVidia Inspector).
So far, so good.... fingers crossed