Since I want to keep things simple, I don't want another keyboard and mouse cluttering my desk, which is where software like Synergy or Mouse Without Borders comes in. These tools allow one mouse and keyboard to be used across several network connected machines. Since I'm cheap, and Synergy costs money, I went with (the free) Mouse Without Borders, which is a Microsoft "Garage" project and available here. It needs to be installed on both machines and I set it up on the primary machine with the keyboard and mouse first. The setup process requires adding the machine name and a key which you get from the first machine to be set up. I had a problem however, which was due to the primary machine not having network discovery turned on. Once I enabled network discovery, everything worked fine and I can move my mouse across monitors to the new M700 PC and back, and use one keyboard with both. It makes sense that network discovery would be needed since it is a Microsoft product, though some option for a direct TCP/IP connection would be handy. Mouse Without Borders also allows files to be dragged and dropped across PC's which is pretty cool. Since I have both PC's connected to the same switch, there is no noticeable lag either - but I would not try to game using Mouse Without Borders.
While figuring this out, I also read that some people suggested manually adding the host and IP instead of letting the program automatically set them up. I tried that during setup and it did not help with the connection problem (network discovery fixed that) - BUT adding the hosts manually does seem to help with reconnecting after one machine is restarted.
To add the PC's manually, go to settings. If you are installing and having problems, you can skip the setup and the settings will then open. In settings, go to the "IP Mappings" tab and enter the hostname of the other machine or machines that you want to share the keyboard/mouse with, and their IP address. There are examples already there which will be removed when type in the box, the format is:
which would look like this:
You can get the hostname by going to the search box, and typing "cmd" which will show the "Command Prompt" app, click that which will open a window with a cursor. Click in the Command Prompt window and then enter "ipconfig /all" which will spew out a bunch of information about your IP address, and other things, but what you need is the Hos Name and IPv4 Address, which may say "(preferred)" next to it. The Command Prompt window can be closed by typing "exit" or just closing it like any other window. You can use the Host Name and IPv4 address to set up the manual "IP Mappings" in Mouse Without Borders like the example above - by entering the info for the remote PC you want to share with. I did this on both sides and it helped with reconnecting.
Mouse Without Borders works when the logon screen is active as well - which would be a problem otherwise.
Update - There was one thing that was bugging me about the way MWB works. Without a physical mouse connected, it did not show the cursor for resizing a window when hovering over a edge or corner. This was fixed by plugging in a mouse to the PC (I just plugged one into the back of the PC). I may try a wireless usb mouse to see if that will make it work.