Very poor graphics performance on new 13" macbook

Just bought a 13" rMBP.

Really poor performance all round. I specifically bought this to get more screen real estate.

Unless you have it at exactly 2x scaling, the performance is very poor, especially in Chrome. Safari is a bit better, to be fair, but it's not great.

On a 4K monitor plugged in (w/ the macbook closed so there's only one screen) graphics performance is like a ZX spectrum. Windows don't move smoothly, everything drops down to single figure FPS all the time.

Wouldn't recommend at all. However, I don't want the bulk of a 15" macbook pro. So I don't really know what to do about it.

You may have a dud - mine doesn't exhibit any of these issues (although only tried with a regular 1080 monitor).

It's not a dud. It's a underpowered GPU. 1080p monitors are fine, it's 4K monitors that pose a problem.

Really annoyed I bought it, my old MBP had a (user replaced) 512GB HDD and 16GB of RAM. The only reason I 'upgraded' was for retina but it is obvious the GPUs can't handle it.