I could buy the 701s at the right price and wanted an upgrade, so the 595s went. They weren't a success though, I really paid the price for buying without trying that time. They were shrill and thin and had no bass. After a while I realised I was going to be happier with something fuller-sounding, easier to drive, and closed. Even fairly quiet PCs make mechanical noises of various kinds, and in my house even the central heating puts out a fair but of background noise, all of which just goes straight through open cans. The 380s have been a roaring success, got them for about £80 when they were on offer from Amazon... love the balance, the detail, and the isolation. And you can drive them with anything.
If you want a taste of what the high end Sens can do but don't like the price the 595s are a good choice. There're a few fairly noticeable midrange colourations but the ear soon filters them out.
My next headphones will probably be open ones since I really want to see what those are like. Senns are on the list; I would love to have HD 650s or HD 600s, but like you said they are pricey.
I finally pulled the trigger on the STX. Thanks so much for your help!