I was planning on building a computer and was originally gong to get 2 radeon r9 270x but when looking through the forums people recommended a r9 280x and i looked at t and wondered if i could drop a 270x in later. so here i am
You can't crossfire cards from different series (5000 series and 6000 series etc.), but you can't CF these two cards, even thogh they're the R9 series, so the answer is NO. Just 280x is very strong, so don't worry.