It's basically impossible to know how much of a difference you are going to get going from one projector to another without real world testing of the models. The Optoma is rated to be about 33% brighter than the TH671ST. That's not actually a ton brighter.

But, the BenQ could have some hours on it, the lamp could have dimmed a bit, and it may not be running in it's absolute brightest mode, which can impact brightness a fair bit.

Not that the TH671 rating of 10 lumens per square foot is based upon REVIEW measurements (real world) vs. the manufacturer's specifications. So, you have a radio button you can click which makes the TH671 into 'manufacturers specs', which changes the number to 31 lumens per square foot.

The numbers are pretty typical, and I'd expect the Two models you list to be brighter, but I haven't seen them first hand and it's pretty tough to know how much brighter they will truly be in the real world. It wouldn't likely be a ton.

The best thing to do in any golf simulator setup, is to use spot lights over the golfer, and to do your best to make the screen area as absolutely dark as possible. This will meaan that most projectors will perform just fine and golfers will be able to see the ball just fine as well.

Foot lumens (FL) are a measure of brightness. Not really a score. Total rated light output of projector, divided by the square footage of screen equals the lumens per square foot (FL) result.