Personally I would never use the xbow on Suicidal/HoE because in my experiences the M14/LAR combo out performs it in many ways. Here is a quick video I threw together, note the total lack of editing skills.
YouTube - Comparing M14/LAR vs. Xbow Post HoE
The xbow simply costs more to be less effective. The only point of the xbow that really shined was its long range, but what good is long range if it is trash when it really matters, when a fleshpound is about to crush you to a pulp right in your face?
Also note that it took less than half the time to take the fp down with the M14 compared to the xbow (with the M14 the fp had just finished its rage animation and I even missed a headshot, with the bow the fp will be charging at you when it still has half health).
With the M14 the fp was taken out without the fp moving an inch, ideal for places without a lengthy view needed to take out a fleshpound with a bow (a distance of at least a good 3 seconds of fp sprint time to cover it)
Last thing worth mentioning would be the ratio of ammo it takes to kill a fp. The massive amounts of more ammo available to the M14/LAR compared to the xbow allows the M14 SS to be more effective for longer and deal much more damage throughout the entire wave to any type of ZED without being as bound to only fleshpounds and scrakes like a xbow SS would be.
EDIT: Actually 10 M14 shots costs 7 pounds, not sure how i messed that up in the video, but it just go to show the massive price difference from the xbow