My specs:
i7 3610qm
Radeon HD 7970m (2 GB)
8 GB RAM
Regardless of whether I run the game on the lowest possible settings (with DX9), or the highest possible settings (with DX11), the game loads very slowly (and often hangs / freezes on loading screens), and it causes my computer to overheat.
Using GPU Temp, a program that monitors the load and temperature of my graphics card, I noticed that as soon as the character selection screen shows after the client starts, the "load" on my GPU is immediately at 99%, and the temperature begins gradually rising until it gets up to 90+ Celsius.
I can't really explain this; my computer runs lots of other, much newer, games without any similar issues. I was playing Dota 2 just before trying to play DDO and the "load" was always down around 40% and the heat never went above 77. I have to imagine there's just some kind of hardware incompatibility with the DDO client for some reason.
Note -- I haven't done any sort of overclocking or such stuff with my GPU. Aside from updating drivers, I haven't done anything to my card.