So are the RJ45 keystone things easy to crimp or impact? Do the wires stay put in there?
The RJ45 wires are a bit thin, so you need to take some care with them. First, you absolutely must have the stranded RJ45 wire - which is used for patch cables. The solid stuff is unworkable for crimping and tends to break too easily.
Since I converted an old non-modular control panel over, in most cases I kept the old wiring in place (22 guage stranded) and just twisted the old wiring with the RJ45 and then crimped it together using an insulated connector. This is not as pretty as directly wiring it but it seemed a lot more secure to me than crimping the thin RJ45 alone. I also secured the RJ45 cable to the board in several places with staples so I could not inadvertantly pull the wires out. So far I have not had any breakage even though I'm handling the joystick panels all of the time.
On the IPAC of things - the RJ45 sockets are designed to take the wire - you basically just push it into place and two thin edges cut into the wire and make the contact. For connections to the IPAC itself, I just twisted the wires together and screwed them down, much as you normally would. In most cases I had more than one wire going into the IPAC (for example there are two JOY1 sockets, two JOY2 sockets and so on so I can map more than one joystick to the same port) which helps to secure the small wires.
One other nice feature - since ALL of the inputs (including the pinball and control buttons on the cabinet) plug into an RJ45 jack, I can actually just unscrew the patch panel and remove the IPAC panel as a complete unit for servicing.
I think the RJ45 is more flexible than an RJ11 - you can support joysticks with buttons, six button panels, or (as I have done) add "thumb" buttons to the joystick panels that align with your six button fighter panels. Plus if you want to wire the control buttons to a control port you may need 6-7 inputs.