Might want to stick to processors listed on their spec sheet;
See how far it can be pushed and still be stable.
Might want to do an assessment of things on a piece of paper and see how much you'll be spending. Upgrading yesteryears tech isn't exactly the best decision, not when that amount would add up to a concurrent system.
The limit they give on the processors is due to the 35W lock. All suggested processors in the list are 35w processors. I have read that this lock can be removed by flashing the BIOS to unlock it. The m920 can take a 65W processor using the same BIOS (From what I have read) So I just need to find the right BIOS files to unlock this. I have not had much success with this since each Bios I have found was specifically made for a specific M720q.
My current BIOS is the latest version and have found a possible earlier version of an unlocked BIOS on a thread that might work. I have however decided that I will be unlocking the BIOS myself instead of leaning on someone else to ensure I do the right thing and not hope someone did the right thing.
With the above done, the power Supply needs to be upgraded. I have found the Lenovo Legion had a 300W power supply with the same plug and also found a Video of someone using one on a m720q. I will also have to upgrade the CPU cooling. The m920 has the exact same "frame" with a 65Watt cooling system as opposed to the m720q 35W cooling system. The Processor I am looking at is a 95W CPU. This will leave me to create my own 3d printed cooling system. I already started with a possible design for this based on Nautilus air movement.
The GPU is the major problem. eGPU's here in my country is ridiculously priced. My original thought of using a Bitcoin mining GPU will work as long as I run it from my PCI. My original plan was to just run it from a type C USB or USB port but can find no reference anywhere if this will work. The Thunderbolt chip on the m720q was not activated (As per many of the threads I have read) leaving me back with the PCI port. This I can do by adding a riser card (Seems to be the only option here). The USB port for the mining GPU onto that and then outside the unit to the GPU Port. reason for going this route is I can add an external PSU to the bitcoin GPU. The video I followed on a similar build, the OP said that the temperatures was very high, and he heard some "ticks" coming from the outside port, but he was able to run games and programs properly without problems. He did not say for how long, however.
For the outside GPU to work I will need to resolve the cooling (again 3D printing and Fans, leaning towards nautilus again) as well as finding a way for the ePSU to switch on and off with the m720q. The switching of the PSU, I am looking into the possibility of adding a 5v Static relay to the USB cable entering the "eGPU". This will trigger the PSU to switch on but have not looked into how to switch it off again. All PSU (of today) has "soft switches" and I will have to look at the plug pinout diagrams to find the on and off switch wires. I have not looked at this yet.
Cost, yes agree. this was one of my biggest concerns. Over investing into something that is not worth it. The m720q is magic. I would say it's major flaw would be the GPU side of things. LP GPU's are available but from what I saw on reviews, LPs pretty much give half the results of a full GPU card. This is why I thought of just going directly for the Full GPU. I will however start off with RAM, Riser, a LP GPU and a 300w PSU to see how far the system can be pushed before pushing into the eGPU side. Unfortunately using a LP GPU takes the place of my SSD space so will have to make a work around for it. The Processor will be just a nice to have. I am currently running in 2C2T and having more just cannot hurt (LMAO).
So far adding the totals to what I have seen available, it seems to be worth it. Here in my country, I can find something similar (once upgraded) for around 3 times more as to what I can build it for. If I go for "just" newer, it is double for what I can build it and then it does not have a "proper" GPU included taking the cost to more than the upgrade (or rebuild)
Thank you for that spec page. I was working from fish diagram that I found on a site a while back.