MacBook – Very small resolution on external monitor Windows 7 with Macbook Pro Retina

@Daniel has a good idea with the switch.

However, if you don't need to share keyboards/mice, I recommend getting a monitor with multiple inputs (almost all these days) and just connecting the Lenovo to one and the MacBook Pro to the other. Switch the inputs on the monitor.
The downside of this is that, even if the monitor isn't using the Mac's input, the Mac will think it's connected. So, you may get windows popping up on a nonexistent monitor, and losing your cursor now and then.

As for features: Make sure you get something with a high contrast ratio, and as VESA mount. Even if you don't anticipate mounting it right away, you may well want to later, especially if you share it between multiple machines.

I would suggest just to use the "more space" 1920x1200 in System Preferences.

From what I can see, options in System Preferences has been tweaked to look better than to just change the resolution with some tools like SetResX or DisplayMenu.

If you don't like 1920x1200, and really want to get smaller, your only option will be 2880x1800. Everything will look small. But you will get used to it.

You might need a larger cursor, that option can be found under Accessibility in System Preferences.

Any other apps you want to have them look nicer, you will need to do it on a per-app basis, font size, zoom, etc.

But it won't be as good as the options under System Preferences, basically, if you have 2880x1800 as your resolution, and have everything 50% larger, that will be 1920x1200. So there's really no point to refuse it. Also Boot Camp defaults to 1800p with a 150% dpi.

The bottom line is, the options built-in are tweaked, you won't get anything better than those. Stick to it. As a fellow developer, I always choose 1200p or 1050p when doing UI designs. Go back to 900p when coding.