emulator lag issue

I recently softmodded my Wii, downgraded to System Menu 4.1U, and installed some emulators like FCE Ultra GX 3.3.4 and Snes9x GX 4.3.2. The emulators have a lag issue; I press a button on the controller and it takes roughly a quarter- to half-second for the input to be recognized, making most games unplayable.

I have seen others with this issue but nothing I've seen recommended fixes my issue. I tried moving the ROMs from external HDD to SD card, I've tried both the classic controller and the regular wii controller, etc. Some have said the type of video connection used makes a difference (I am using composite cables) or changing the video output mode might help (my Wii is outputting 480i to my HD plasma screen; incidently the 480p otion is greyed out so I can't even try that) but regular Wii games play just fine without any lag - shouldn't ALL games have lag if this were the issue?

I'd greatly appreciate any other ideas to help me fix this issue.