That's likely to get real hot with the number of XM-L's in there. Each one is 3.35*3=10 watts. A very approximate minimum is 1 square inch per watt, so you're looking at 110 square inches. Of course that changes greatly based on fin shape, surface finish, mounting, and airflow. You might want to look into the heat transfer equations for fin efficiency, or model it after commonly available heatsinks on the market. It looks like you found a heatsink that you could stick on the back of the housing.
Aside from that, your design looks very sharp as in you could probably get cut pretty good on it, and make sure to account for the internal radii on the lens pocket unless you are using some kind of extrusion for that part as well.
I can probably give you some better input if you describe what type of offroading you will use it for. Rock crawling, trails, fire roads, etc? From my experience building offroad dirtbike lights, you don't want to think too much about lumens too much. I would definitely use a warm or neutral white LED since they make the trees and dirt look warmer and more realistic, producing less glare and it's just easier on the eyes. Also, based on the way we perceive light, you can only slightly tell the difference between, say, 2000mA and 3000mA. I would consider running them at below the maximum rating since it will reduce the heat thus last longer, but still be very bright.
Regarding the driver, does the RZR have a 12V battery? In that case, you need to consider the running voltage, usually 13.5-14.5V, and the voltage of the LEDs, and try to match them closely while still being less than the source to account for resistive and driver losses. 11 XM-Ls is kind of a weird number, because you will have to wire 3 or 4 in series to match the source, and 11 is divisible by neither of those. Side note.. I actually just bought one of those drivers and it burned out for no reason. It was working great for a few minutes, didn't get too hot or anything, and just stopped working. I don't know how robust it really is. You might want to look at a linear regulator. DIWdiver made a neat low dropout (LDO) linear regulator that might be useful for you. Anyway, good luck. Feel free to ask questions.
