You all already know that the Chronic Dev Team is working on a new untethered jailbreak solution that it will release in the near future. You know that the exploit they used in this version was blocked by Apple in iOS 4.3, so they have no reason to postpone the release since they won't be able to use it on iOS 4.3 anyway. I didn't know the list of devices compatible with greenpois0n RC5, but on WikiPedia some information has been published that reveals the terminals we will be able to use.
iPhone 3GS, iPhone 4, iPod Touch 2G/3G/4G and the iPad tablet will have an untethered jailbreak on iOS 4.2.1 from the Chronic Dev Team. Interestingly, the iPhone 3G is not included in the list, but for it redsn0w does untethered on iOS 4.2.1, so you don't have to worry. That list also includes the Rubyra1n jailbreak solution that was attributed to geohot but has not been confirmed by him yet, so don't get your hopes up that it will be released after February 10.
I don't know who published that information on WikiPedia, so take it as a rumor for now, although in essence it should be correct.
