Hello my friend!
Did you solved this?. I'm experimenting the same problem on an intel motherboard, very frustrating to deal with it. We have reduced memory consumption more than half (both in CPU and GPU) and still the same problem. Texture compressions helps... only a little.
NO. We still don't konw how to resovle this problem.
Don't know is thsi yet usefull for you but... try windows 7 with the smae drivers and you will see no more handle leaks. Of course, porting everything from XP to 7 is a lot of wor, but it's up to you consider thar. If yo uhave another advice please let me know.
Goodbye! Good Luck!