We have two BR pullets at 7 weeks right now and that looks like a pullet to me. The thing that worries me a little bit is that at 5 weeks it hasn't grown in it's neck feathering, and males usually take longer to do that than girls. But, I'd still lean towards pullet.
I also have 7 week old chicks and I think its a pullet! I've also heard that male are lighter and I have one who I think is a roo! I"ll try to post pictures tomorrow!!. I'm pretty sure he is a roo though! He (or she) is much lighter than the rest though!