I've been playing with a UHF VP6000 and also own a 7/8 VP6000. In addition to those, I rock a VM900 in my pickup (with a UHF 5300 to round it all out).
A VP5000 is literally a NX5000 portable running Viking firmware. Don't believe me, run the VP5000 FCC ID...it'll return as a NX5000. Con of course is you don't get DMR or NXDN support on the VP5000. Pros are better trunking performance and you are dealing with Armada and not D1N. Armada is built around the maintenance of radio fleets (like Motorola's Radio Management but IMO more feature rich). To the end user...there OTAP, kiosks and even WiFi are all methods which Viking radios can receive codeplug updates and firmware updates.
The VP6000 is literally a NX5000 with a top display in a flared chassis running Viking firmware. Again, check the FCC ID.
As far as how the radios perform...I think the noise cancellation is better and the audio quality is better compared to an APX. Sensitivity wise...having tested thousands of XTS and APX portables over the years, the VP6000's I have basically perform the same for SINAD and BER.
Full disclosure...a glance at my title should make it pretty evident who is currently signing my paychecks. That being said, even if that was not the case I would continue to use the products over APX as long as I had that ability (i.e. not forced onto a single vendor system).