I bake pound cakes only in tube, bundt, and loaf pans, because I prefer actual slices of cake. I would suggest that a pound cake baked in a sheet pan be tested starting @ 25 minutes for the level of doneness preferred, and and to make sure it doesn't overbake.
Barb, in my 8x8 pan, I bake it at 325 for 45-50 min. It's the cake I use for pineapple upsidedown cake. It comes out nice and moist. I'm not sure how to adjust for a 9x13. It would be thinner, so less time.
I think a typical pound cake recipe baked in a 9x13 would be too thin to be pound cake no matter what temp you used to bake it. It would be all crust. Maybe a double recipe would work, but I've never tried anything but loaf pans for my pound cakes because I like the slices, a bit of crust covering moist cake.