I know what you mean my Vostro from a few years ago is still a decent spec (i5-2430/16Gb DDR) however I found out today you can now get the X1 Carbon with the 2560x1440...my Vostro is looking more and more like it needs replacing.
If you're a developer - take a look at the keyboard first. They replaced the F keys with capacitive buttons (ie. touch sensitive buttons as opposed to physical buttons) and the capslock key was split into a home/end key instead. Sure it's still a nice laptop, but that sort of thing would drive me crazy.
I would check out the X1 Carbon in person before making that decision. The display is terrible. It's the only device over ever used that's given me significant headaches after even moderate use.