[coreboot] T520 vs. T530

Hello guys,

I am planning to buy a used Lenovo Thinkpad and install coreboot on it. I am completely new to coreboot and I need help in the decision if I should buy a T520 or a T530. I read the wiki and some other pages but it's still hard for me to decide which model I should buy.

1. I need CPU power. I read that it is possible to put a i7-3940XM in a T530. Because of coreboot it should also possible to put it in a T520?

2. I would like to use an eGPU. Any differences between these two models?

3. With which model it is easier to install coreboot on it?

4. What are the general pros and cons of a T520/T530, especially with coreboot?

Thanks for your help!
Kind regards