You'll note that the white point color temp is virtually identical in all modes, and always just a touch cool.
Going from mid-point on the zoom to full telephoto (it's really not far to go) drops the brightness by about 3% to 1726 (for Bright mode) Going from mid-point to full wide angle increases brightness by 3% to 1832 lumens. In other words, place the projector where it fits best, and don't worry about the minor difference in brightness.
Switching to "low lamp" which Vivitek calls Normal, from "high lamp" which they call Boost, results in a drop of only about 15% (for Movie mode that's 683 lumens down from 806 lumens).
Since this projector is especially bright many will actually use the lower power mode, and get a 50% boost in lamp life to 3000 hours.