Suggestions for what to replace my Cree XM-L2 U3 - maybe a steap up??

Well…
brighter is always possible - your XM-L has roundabout 1000 Lumens - the Emisar D4 has 3300 up to 4300 Lumens.

But first things first: What do you need that light for? More throw or for close-Up Work? Which battery-type? What batteries are available?