At what you're looking at, I would recommend the t450. The screen is so much better than the t430 and the keyboard maybe worse but i wouldn't sacrifice reliability to a mod. The lenovo outlet has plenty of great deals all the time.
Just doing a quick outlet search gives me a 671$ t460s laptop with an i5, 8gb ram, 128gb m.2 storage and an IPS 1080p LCD. Upgrading from an x200, you will almost absolutely need an s series laptop because otherwise you will feel like you added a brick to your bag. Also, GET THE INTERNAL BATTERY. I made that mistake on my x240 and regretted it. The battery life with a slim without the internal sucks.
You can get better deals then this, It's just a waiting game. A good few hundred laptops come in every few weeks. Since I don't know your budget, i can't tell you if this is good or not. Also, a more modern bios will help with triple booting, a feat itself.
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Welcome to the jungle, we have FrankenPads
If you want it you're going to bleed, but that is the price to pay
And you're a very rare mobo, very hard to get
You can see the blinky lights, but you won't get them for free.