The bumper itself probably won't cause a sag at least anything you will notice. Most that sag have the heavy winch on it also.
Also it depends on the coils you have under it. Look at your front coils and there should be a tag on it. Look at the last to numbers (there will be two letters at the end, ignore them. You want the last two numbers)
If you have lets say 13, 14 or 15's they are real weak coils and they are the ones that sagging can occur on. 16-17 are a little stiffer and may sag a little with a winch. While 18-19's are stiff enough to handle the heavy items with no sag
I had 14's on mine and it sagged 1.25" but that was with the XHD and 95 lb winch. I put 19 coils on and it took it out plus raised mine a little on top of it.