The Quick Verdict
Get the Optoma GT2400HDR. On the numbers that matter for a sim build, these two are identical: throw ratio, input lag, and the screen shapes Optoma lists. The GT2400HDR lists at $1,599 and the Optoma ZK431ST-B at $2,699, an $1,100 gap at list. That money buys one headline difference. The ZK431ST-B lists a 3840x2160 resolution, where the GT2400HDR is 1920x1080. The ZK431ST-B is also rated 100 lumens lower. It only makes sense if that resolution figure is a must-have for your bay. Check price at The Indoor Golf Shop →
What They Have in Common
Both have the same 0.496:1 fixed lens, with no optical zoom and no lens shift. Both have the same 16.7 ms input lag at 1080p 60Hz, keystone of horizontal and vertical +/-15°, and a laser light source. Each is natively 16:9, with 4:3, 16:9 and 16:10 as stated modes. Both are 2026 models. Optoma doesn't publish a golf mode, a light-source life or a warranty term for either one.
Where They Differ
Throw and image size: a dead heat
Image width is throw distance divided by throw ratio. From 10 ft back, each one gives a 20.2 ft wide image (10 ft ÷ 0.496). Run it the other way and each needs to sit 5.0 ft from the screen for a 10 ft wide image.
Neither lens zooms, so you get no slack. The mounting distance alone sets the image width. Measure from where the lens will sit to the screen, and that number decides your image size on either projector.
The one lens figure that differs is the offset. Optoma lists 116% +/-5% for the GT2400HDR and 114% for the ZK431ST-B. Check that against your mounting height before you drill.
Screen shapes
Both list 4:3 among their stated modes, and that's a common impact-screen shape. Square 1:1 isn't among the stated modes for either one. That doesn't mean it can't be done; Optoma just doesn't list it. The answer is the same on both, so it doesn't separate them.
Brightness, lag, golf mode
Both are rated to ISO 21118, so the figures compare directly. The GT2400HDR is rated at 4,200 lumens and the ZK431ST-B at 4,100. That's a 100-lumen gap in favour of the cheaper one.
Input lag is 16.7 ms on each at 1080p 60Hz, so there's no gap. Optoma doesn't say whether either has a golf mode.
Resolution, and what $1,100 buys
This is the real split. The GT2400HDR is 1920x1080. The ZK431ST-B lists 3840x2160. Optoma doesn't say how that's produced, so I won't call it native or pixel-shift. I haven't seen either one running, so I can't tell you what the difference looks like on a hitting screen.
Beyond resolution, the ZK431ST-B is 0.31 lb lighter. Its listed dimensions are 10.8 W x 4.3 H x 8.5 D, against 10.79 W x 4.49 H x 8.50 D for the GT2400HDR. Call it a hunch, but on a ceiling mount neither difference is going to decide much.
Who Should Buy Which
Get the Optoma GT2400HDR if:
- You want the same throw, the same lag and the same stated screen modes at the lower list price, $1,599.
- Your impact screen is 4:3 or 16:9. Both shapes are among its stated modes.
- You want the higher of the two brightness ratings: 4,200 lumens, ISO 21118.
- Your measured lens-to-screen distance and mounting height work with a 0.496:1 fixed lens and a 116% +/-5% offset.
Get the Optoma ZK431ST-B if:
- A 3840x2160 resolution is on your must-have list for the bay, and that's worth $1,100 at list to you.
- The 114% offset suits your mount height better than the GT2400HDR's 116% +/-5%.
- You're fine giving up 100 lumens on the same ISO 21118 rating to get that resolution figure.
The Bottom Line
These two share the same lens, the same throw math, the same 16.7 ms lag, the same stated screen modes and the same laser light source. The GT2400HDR lists for $1,100 less and is rated 100 lumens higher on the same standard. The ZK431ST-B's case rests on a 3840x2160 resolution figure that Optoma doesn't explain further. If I had to bet, that $1,100 does more for a bay spent somewhere other than the projector.