I'd forgotten about the Momentum. They do look very good, if a little pricey; but then Sennheiser has upped the price of their higher end products. The HD650 was about £180 six years ago, now they are about £280. £335 on the jungle site! My word. Now that is a monster price hike. As good as they are, I've have seen comments from some who own them, think they are not worth £280, let alone £330+. Those that paid £180 a few years ago, must have smiles on their faces. 
Not looked into the MDR-1R at all. £160 on the jungle site looks interesting indeed. Trusted Reviews, had them priced at £300 and they are £300 on Sony's own site.
Now you say you don't need much bass, but if that were the case, then the K550 would have appealed more than they did. I assuming you got a good seal though, when I say that, as that is paramount. No seal with the K550 will result in poorer SQ.

Not looked into the MDR-1R at all. £160 on the jungle site looks interesting indeed. Trusted Reviews, had them priced at £300 and they are £300 on Sony's own site.
Now you say you don't need much bass, but if that were the case, then the K550 would have appealed more than they did. I assuming you got a good seal though, when I say that, as that is paramount. No seal with the K550 will result in poorer SQ.