Based on this thread, Nichia E17A/E21A series (April 19th: updated with output tests in the OP)
I’d say you want to stick with 3 amps or less. That appears to be the sweet spot.
I’ve used l4p’s A4 model for mine. I’d recommend you, select 2-3a if that’s where you want it to be.
https://led4power.com/product/ld-a4-2-12amp-17mm-constant-current-led-flashlight-driver/
To be honest, i’d encourage you to use the s2+. Manufactured lights are more difficult to work with.
What size is the mcpcb that the led is on?