Honestly, I've never used any of the GC emulators, so my opnion probably doesn't matter too much. However, after saying that, I think the newest beta should be released, even if it is slower than the current release. If people are willing to play MP1 (or was it MP2?) for 4 hours at 5-10fps, then I doubt a few frames are going to make a big difference to them. Besides, they can always use the older versions if they want a slight increase in speed.
On the other hand, if it is slower, then expect to get even more people complaining about it. I understand that current PCs simply can't handle emulating the GC, so I don't use the emus, because I see very very little reason to play a game at 2fps. Nonetheless, with the way CPUs and such are developing, I'm sure that PCs will be able to handle GC emulation in 5 to 10 years. Yes, that may be awhile, but compare it to most other emulators. I wasn't around when ZSNES started, but my understanding is that it took at least 3 years for it to be really really good and compatible with a large number of games. 6 years (as I recall, I could be very wrong) for it to emulate the FX chip properly (for Starfox). Megaman X2 and X3 used the C4 chip for compression, and that took a long time to emulate (years, at least). So, the fact that the GC emulator works as well as it does seems fine to me. Just give PCs a few years to catch up. It's not much different than waiting for the SNES, PSX or N64 emulators to be compatible and playable with a majority of games.
That's my thoughts on the subject. While I highly doubt I'll use the next release, I still think it should be released. I like to see the progress that it makes. And eventually, PCs will catch up. So, I'll probably use it then. Glad to hear that it's definatly progressing though. Mouser X over and out.