The NTSC version is working fine for me in Nestopia. It's possible the sound is distored and I haven't noticed because I don't know what it's supposed to sound like—but I'm definitely not getting slowdown (and I think it sounds really good).
I'm also using OpenEmu, but it's a build based on 1.0.4 because I'm weird and run an ancient version of OS X. My Nestopia core is based on Nestopia v1.49 r967.