Alright so I did a bit more testing today with the latest version of MAME (0238b) and can confirm it seems stability wise, linked play has improved. It's not 100% but it is better. Below are the specs of each machine and their network configuration.
DesktopCPU: 3900X
Motherboard: AsRock x570 Steel Legend
RAM: 16GB @3600MHz
GPU: 1080TI
Network: 1Gbps LAN connection, to 8pt TP-Link Gigabit Switch, to Actiontec ECB7250 2.5Gbps MoCA Adapter, to 1Gbps Router
Media Center PCCPU: 7700K
Motherboard: MSI z270 GAMING M7
RAM: 16GB @3200MHz
GPU: 1070 8GB
Network: 1Gbps LAN connection, to 1Gbps Router
LaptopCPU: 7700HQ
Model: Alienware 13 R3
RAM: 16GB @2400MHz
GPU: 1060 6GB
Network: 1Gbps LAN connection, to 8pt TP-Link Gigabit Switch, to Actiontec ECB7250 2.5Gbps MoCA Adapter, to 1Gbps Router
Overall it seems launching the game has become less stable in this version of MAME. Almost every time I'd have to restart the ROM (Shift+F3) once or even twice to get the game to fully boot. Now I did incorporate the FFB plugin in each of the instances. Even though only my MCP had my steering wheel connected to it. So that is a possible factor, doubt it though. Once fully booted the single player stability matched that of previous versions. I do need to play with it more to confirm that. I also noticed that about 50% of the time the non button/front panel display view (Screen 0 Standard (4:3)) would not stick even though it was set in the .cfg file. I could simply set it back to the way I want but was a bit annoying.
As for link play. Nothing has changed from my previous guide for setting up multi machine link play. Once the adapter is set in the .cfg file for the game, MAME immediately picked up my TAP network adapter. In game dip switch and service mode configuration is the same too.
Now into the meat. For each test I was starting the game on my MCP first to make it the host being that it is the highest clocked system I own. After that it was a mixed bag on who I would join second and third. I could get all 3 machines to detect each other no problem. My desktop and MCP seemed to be the most stable but my laptop dropped every time in all of my tests. This seems to confirm my theory that if your machine is too weak and can't emulate the game at 100% all the time it will get dropped. As for when it just depended. I made a video showing all 3 running on the same screen. This was probably the best run my laptop made out of all the tests I did. In the video when my laptop crashes you don't see the sync % drop from 100% but in some of my previous tests you could. The other two machines are pegged at 100% sync. Note: In the video I forgot to turn on the sync OSD on my MCP.
This is defiantly a step in the right direction. There still needs to be a bit more optimizations for this to be rock solid for most but it seems like you might actually be able to get one or two full games in without either machine crashing out. I'd like to see what performance impact or even possible improvement Bigtymer's 60FPS variant will have but will just need to sit patiently and wait.