The D4 is meant to get as much light as possible out of a very small 18650 light.
With a good battery D4 is pushing around 5Amps in to each LED before it ramps down. The D4 doesn’t have much mass to soak up the heat coming off of the massively overdriven LEDs. Toykeeper’s new firmware will help but there is no getting around the physics.
If you need longer runtimes on turbo you need a bigger light. The D4S is better but will still get hot and ramp down. The 219C version has turbo limited to 80%. XP-L Hi will be brighter but has low CRI.
I’ve got a BLF Q8 which is a little brighter and doesn’t heat up. I don’t like it as much as the D4S though.
The 219C in the D4 and D4s is 90CRI, 5000K. That is pretty close to daylight white. As a rule, cooler tint bins are brighter per watt.
I ordered my “Sandy Brown” S2+ with a warm 3000K 70CRI U4-7A XPL-HI emitter. The light is odd-yellow looking and not especially bright with the original 7135x8 driver. I’ve decided to keep the emitter because it complements the body colour.
My bargain grey S2 came with a cold 6500K-7000K XM-L2 U2. I found it very cold and harsh. It was cheaper to buy the entire light than a bare host. It now has a 5000K 219C and a BLF A6 driver. New AR glass too because I broke the original during the emitter swap.