I'd spend it on something that helps your mental health. I worked in a very dreary office under a lot of stress for a long time before I realized I could change my environment. I'm still doing the same work with the same equipment, but the walls are a color I like. The desk is comfortable. I have green plants to look at, and nice things on my wall. I have funny action figures on my desk. I spent my time and energy making my workspace nicer and it makes dealing with workspace stress a LOT easier.

I just ordered the new Acer Predator gaming laptop and monitor (total $4200, Newegg). Curved 30" UHD NVidia G-Sync display with eye-tracking. Laptop sports NVidia GTX 1080 with 8GB video ram. Shooting for smooth 60fps 4K real-time rendering.

After that, next on the wish list would be: HTC Vive, GoPro 5 Hero, a large format (55"+) OLED UHD display, and perhaps the companion Predator gaming tablet (8", HD). Also need software: Abode Creative Cloud, Autodesk 3DS Max. And if there is anything left: Anki's Cozmo Robot for giggles.

I'd scrap the MBP and get a 5K iMac instead with that amount. Personal opinion, though.

5K iMac + two P2415Qs is what I'd ask for. Depending on how much travel/client meetings maybe a tablet or cheap compact laptop.

My new Windows 7 PC has an Intel WX58BP Motherboard and an Intel X5677 CPU, precisely because of the ECC support that "lazylizard" mentioned. Crucial ECC RAM modules would also be highly advisable. A system built around that core configuration will be highly reliable. I actually bought a spare motherboard too, to extend the lifespan to at least 12 years.

Spend a bit of money on some desk plants. My desk looks like a little rainforest. All the extra green keeps you happy, you get a bit of extra oxygen, and gives you something to take care of to distract you from staring at nothing but your screen.

Beyond that I'm shocked no-one has mentioned getting either the comfiest chair you can find, or a standing desk. Either of those two will make a night and day difference.

I'd get an iMac rather than a MacBook pro.

Really have to know what sort of engineering you're doing....I have four monitors now, so that's what I'd recommend. If you're an iOS developer, get a Mac. If you are doing a lot of video processing, get a few graphics cards and build a PC...

For video processing I'd recommend a Macintosh as well.

Video processing wasn't a good choice of terminology; what I meant was something like Unreal Engine.

Custom built Ryzen Desktop with a high end gpu? and one or two 4k monitors maybe

something that takes ecc ram and can use zfs?

Adjustable sit-stand desk.