Having similar problems, unfortunately. Major slowdown when accessing inventory and changing or moving items. Voice clips take a good 3 seconds or so to start. Portrait selection on the chargen screen can freeze the game for about 20 seconds.
Windows 7 64-bit
Intel Core i7-2600
ATI Radeon HD 5700 (driver version 8.961.0.0)
16 GB RAM
GOG version, installed to C: drive.
Output log is from opening the game, quickly clicking through chargen to tab through some portraits, then returning to the main menu and loading an old save to fiddle around with the inventory. Major slowdown was experienced in both. http://pastebin.com/1nQG5wZS