I think we would need to know a lot more about how you are using your Mits 4000hc. Room dimensions, screen size, lighting conditions, your future plans (for example to use on porch, in living room.) What do you like about the mit's 4000hc and what do you not like about your current PJ. Why are you thinking of upgrading? How many hours on bulb do you have? Because then the guys can comment whether FOR YOU, it would be an upgrade or not. If you are only in bat cave and the picture is bright enough for you, and the bulb is plenty bright. Maybe hold off.
Would you like the option of 3d, occasionally? Where is your PJ mounted right now?