I purchased a factory round relay and socket from PP for my low beams. Then again I am running 80/100w H4s. WOW what a great setup.
Unless you do quite a bit of high-beam driving. I wouldn't worry about the high beam really. I don't have one. Then again, I am conscious of not running my high-beams. I still flash though!
I believe the factory ran 55w low beams. If you want to take advantage of all that you can, get the relay. If not, I don't think you NEED the relay. It will save your headlight stalk switch from burning out in a couple (or ten) years.
Have fun!