Look, K 450 is based on the same drivers as infamous K 26 p and k414 p(and also k 24 p and k 412 p), even though k 450 is refined, more comfortable and luxurious version of them. It's widely regarded that k81\k518 is much better pair of cans than k26\k414. In my opinion, even if k518 technically better, the k26p\k414p is considerably better portable cans due to extremely high sensevity and good driving sound. Also, the k518 are very uncomfortable.
So, if you can take the k 450 for a good price, or at least for k518 price, i say go for it.
Also, if you don't need isolation, go with k 420 or whatever blue open model is called. It sound really good as a successor of great k 24p\k512p.