Best price on Panasonic PT-AE8000
I've run the Chief mount with both the 4000 and 8000. It's my go to mount for every install. As for the "upgrade" I'd say the 8000 is a decent evolution of the Panny projector and will net you some increased brightness. If you want a bigger screen, need/want more light output, and/or are in need of a new bulb for the 4000 then the price of the 8000 is probably worth it. If you are happy with the 4000 and aren't looking to increase brightness or screen size and or have extra bulb(s) stashed then I'd wait to see what comes down the pipe in the next 12 months. The Epson LS10000 and 9600 look pretty interesting and we know that JVC and a Sony are battling in the +$5000 market, and 4k in sub $6000 range is probably gonna happen in the next 12-18 months.
DIYSOUNDGROUP Special 88 LCR and 2x Sealed Dayton 18" HO (iNuke 6000 DSP)
Niles Stagefront Pro870FX Surrounds
Onkyo TX-NR5010, Denon 3313UDCI, AppleTV, PS3 - Panasonic AE4000/Draper ONYX 110" 16:9
Chief MFG mounts, Sanus EcoSystem Rack, Tripp-Lite SmartOnline UPS
iRule/Global Cache system control, Atlona HDMI/CAT5e distribution