The Lenovo Thinkcentre M720Q and M920Q have both an m.2 M key and an internal PCIe x8 slot you can stuff a GPU, quad gigabit or dual 10GbE into. No ECC though. Sells for about $100 on eBay for a decent one with PSU that is the same PSU as their laptops (Bonus if you're a Thinkpad user). You need a riser and rear bracket for the PCIe slot that can be found on eBay for like $25. I have a 6 core i5, 32GB RAM, a dual Intel 10Gb adapter and 2TB NVMe in mine. Idles at 19W which is 2W less than the rectangular trash can 10Gb Verizon router's 21W. Total build cost was around $200 for all used hardware.
The lenovo m720q is amazing little machines. I’m using it with a 2 x 2.5 gbps QNap nic and running OpnSense. It’s been almost a year and it has been rock solid as a router. Before I discovered the m720q , I had no idea that a 8 lane PCie slot was possible in a mini-pc that small.
I have a 4x1Gb i350 in my SFF EliteDesk and it can get quite warm. I've had to install an aftermarket small fan for peace of mind, since the case only has a CPU and a PSU fan which don't create any airflow over the extension cards.
How's a dual 10 GbE faring in the even smaller enclosure of those Lenovos? What's the noise situation? I wanted to switch my router and random home VM needs to an EliteDesk mini I have lying around but it only has a Gb port, so I was looking at thunderbolt 10 GbE adapters, but seeing how pricy they are, might as well get a new complete box.
I've yet to really beat on it but it's quiet for its size with a typical laptop like fan sound under load. The dual port 10Gb intel nic doesn't seem to add much heat though I purposefully went with an SFP card in order to use cooler running fiber SFP's (A copper SFP runs burning hot vs a warm fiber SFP).
A brand new dual port 10Gb SFP card costs like $100 USD. Used is far less. I also wound up realizing that when it comes to 10Gb, copper can be more costly than fiber and uses more power per port. So I only buy SFP+ gear so I can use one of many interfaces: copper, fiber, DAC, etc. Fiber and DAC cables are cheaper and use less power. I have a ~$250 USD 8 port Mikrotik 10Gb SFP+ switch and also bought a few cheap 10Gb mellanox SFP cards for my server, desktop and work bench PC for like $30 each off ebay (I use them in Linux and FreeBSD.)
