the universal ones can usually be used in either position would just check the specs to make sure, the problem with that link is that the description says horizontal and the specs on the same page say base up only so obviously one or the other is wrong.
if you are using 1000 bulbs would probably choose from these 2

GE Philips Sylvania EYE 400 Watt Metal Halide Lamps Light Bulb
400 Watt Metal Halide Position Oriented Light Bulb