D3D Slowdown

[Kurausukun]

Whenever I play Kirby's Return to Dreamland with D3D, I get massive frame drops. It plays perfectly smoothly on OGL, but the Dolphin has issues rendering the shadows on OGL (therefore this is the only game that I have to use D3D for). I am playing at 3X internal res, but even though OGL works better than D3D with Nvidia, I thought my graphics card would be more than powerful enough to emulate it at full speed. Is this performance expected, or are there other factors at play that I should be looking for? Also, I disabled the XFB altogether since I don't play the minigames, if that's at all relevant.