Big, I don't know. The only folks I've ever seen using a latern just used a coleman for catfishing. Seems like it should work fine, quite too. The only draw back I can think of would be the heat.

Dog, It all depends on how much you use the troller (if they're on the same battery). Our experience was about 4 hours for two 150 watt halogens on an inverter. So a couple of 55W driving lights should last a bit longer.
Usually we see more fish at the surface at night. Usually! Some nights they just seem to go away for a while. Many times I've seen a bunch of fish for a while and then for some reason they just seem to all disapear. If you stay out long enough, they show up again. Why? I wish I knew. I'd just take a break then also. LOL