The XHP70 (datasheet) can be wired for 6V or 12V. It is rated for 4800mA at 6V and 2400mA at 12V. (~30W) Whether or not the MCPCB is the “direct thermal path” (DTP) type will effect the achievable output. As always, the best thermal path is achieved with a copper DTP MCPCB. If you have an adjustable power supply: use a lux meter or measure the voltage across a photo diode to determine at what current the light output peaks. This will be the absolute max reasonable drive current. You should be using a constant current power supply.
Here is Djozz’s test of an XHP70 on a copper DTP MCPCB: Cree XHP70 up to 4022 Lumens and XHP50 up to 2546 lumens - Multi-die leds. - #576 by djozz
XHP70 is a quad die LED with large gaps between the dies, so it is probably a bad choice for that optic. Also there is the newer XHP70.2 which has much better performance: LED test / review - Cree XLamp XHP70.2 P2 40E (4000 K) - The second generation of extreme overcurrent and light flux capability?
SBT90.2 is the throw/luminance king at this point in time and would be the ideal LED to use.