HP's ZBooks? You can even replace almost any component inside. I got the first generation model (15") and it's very good. Sure, it's not light and slim.
The X250 is pretty good, though you get a keyboard at random and will need to replace the part (always get next business day warranty) if you get one of the junk ones. Otherwise it's a nice laptop - I've not seen anything I like more (though it could be better, of course; a 3:2 screen for starters).
I've used a T450s, and the keyboard feels fantastic on it. At 3K res it'd probably real nice. Unless you need a specific CPU/GPU, stick with the X260/T460s (s for slim). Perhaps compare reviews to the X250/T450s to see if it got worse?
Assuming you don't need high-end power (like quad core), it's more of a preference if you want a small 12" or a larger screen. I dock my X250 and it seems fine, even driving a higher-pixel external monitor. I'd go for the X260, but if software support was better for hiDPI I might consider the T450s. (If they had centred keyboards without numpad, maybe even a 15" model.)
Edit: FWIW when using it in laptop mode, I run CPU throttled to 50% or less to keep it cool. I have the cheaper i5-5200U option and it's fine for emacs/VS/browsing. At full power it can play Dolphin emulator Smash Brothers Brawl and Melee at full speed, but just barely.
The X1 Carbon is much cooler but also less powerful ;)
On some Lenovo models they are the same size (and can be swapped), but not on the Carbon X1.
I'm not too concerned about Superfish - that was only the consumer junk, right? The BIOS-Windows-auto-install stuff was more concerning. But hey, little choices. Lenovo is certainly incompetent - look at the X240/T440 with the terrible pad design they backtracked on (obvious). Or the Carbon keyboards they ended up ditching.