A while back I had a GPS groundspeed of 176kts whilst cruising at FL100 in a crappy old PA38! IAS was just over 80kts. I kept the F215 for that day - quite something. Like stiknruda I now get a 440kt groundspeed at work even with no wind but thats cheating!
I think the biggest gs relative to cruise speed is better than outright gs, it sort of feels more exciting!