There isn't any specification of what is required with regards to CP level that I can see in my writ quest... it asks for a rubedite greataxe, well, with that level of ambiguity, a CP150 would fulfill that request would it not?
I figured it out as well but I thing for the sake of everyone on the forums it is useful to post an answer. NO, they do not have to be CP160. I thought this very thing and was very hesitant to gold the item in fear of it needing to be CP160 and not CP150. To my relief and honestly surprise, it is only required to be CP150.