W1000 Lens Throw
The manual lens has a 1.2:1 zoom ratio. - typical for most DLP home theater projectors. For a 100 inch diagonal, 16:9 screen, the projector (measured from the front of the lens), can be placed as close as:
11 feet 6 inches, or as far back as:
13 feet 10 inches
I should note that the BenQ W1000's lens is apparently different from the Vivitek's in that the projector positions a little less than a foot further from the screen, with the same lens positioning (full wide-angle or full telephoto). According to BenQ, the lens also likely contributes to the brighter image of the W1000 compared to the Vivitek H1080FD.
This type of throw distance is also very typical for a DLP projector. This gives you just over 2 feet of placement flexibility for a screen of that size. Looking at a larger or smaller screen, you can calculate the distances easily from the numbers above. (A 10% larger screen - 110" diagonal would have distances 10% greater for both closest and furthest away...) Note: BenQ indicates that distances and offsets are approximate, that component variation can alter numbers by up to 5%. (5% is probably way over the top - that would be a "miss of about a half foot in the maximum or minimum distances).
W1000 Lens Shift
The W1000 lacks any adjustable lens shift. This BenQ projector has a lot of lens offset (more than the Vivitek). That means that if ceiling mounting you will be placing it above the screen surface top. For a 100" diagonal 16:9 screen, that would be almost 8 inches above (measured to the center of the lens). It also means that the projector can be placed on a table below the bottom of the screen surface (by the same amount). Obviously, the larger the screen, the more offset.
Officially the projector claims an offset of 374 mm. for a 100 inch screen. That works out to placing the center of the projector's lens just under 7.4 inches above the top of the screen surface (when ceiling mounted), or 7.4 inches below the bottom of the screen if on a table top. That's a healthy amount of lens shift, and can be a problem if you have low ceilings, and want a screen much larger than 100" diagonal.