I use an i7 IPS x230 (ie top of the line at the time) with Linux for dev work. It's great. I have the 9 cell battery (but it's getting old, I only get 60% of the full capacity when full nowadays), and I can still achieve 6-7h on WiFi. It hovers around 8-11W with i3wm. Powertops is great at optimizing power usage.
I replaced the ssd because the 180gb intel that came with it has issues with heavy writes and it freezes. In a very Applesque way, Lenovo and intel always ignored the problem, even more so that most of these machines' leases are over and not under warranty anymore. Ssds are cheap these days so not too bad.
Anything else for that laptop is very affordable. Spare parts are plentiful, I got two docking stations with 2x HDMI and 2x dvi for 30$. A genuine charger is 20$. A new keyboard is around 40$ (you can install a backlit one if you want.) It does usb3. The WiFi is slow in my opinion (802.11n) and you can't upgrade to ac without either installing coreboot or buying a modded bios from the bios mods forum (for the price of a 10 USD donation, I'm told.) the intel me can be fully disabled on that machine with me_cleaner (ie reduced to a few dozen kb instead of the original 7mb.)
It's lightweight, very sturdy (magnesium cage), fully repairable (service manual freely available), you don't need anything else than a Philips screw driver to completely disassemble the machine and replace any given part. The only downside is that the to left corner is weak and is broken on most of these, but it's not really an issue if you use the notch or right corner to open and close the machine instead.
It can be had in good condition for 300-400$ and takes up to 16gb of ram (haven't tried 32gb, don't know if it would work) and should last you quite a while.