I enjoy my WM800 mic. I use it mainly with the APX NEXT. It has a really good battery life and form factor. One caveat I have seen in use with standard APX (non-NEXT) is that you cannot transmit on analog channels. You can receive just fine, but transmitting is a no-no. The NEXT line allows full use of analog on the mic. This could be an issue for you, possibly if your use case involves talking on analog.
Also should let you know that connection to non-NEXT radios was supported in a newer FW update for the mic. If you are buying the mic from Motorola or even a dealer, then it should be fine, but if its second hand then it may not have new enough firmware to work on an 8000. FW can be bumped very easily, but it requires a NEXT radio, as that is the "computer" that the mic gets its FW from.