Yeah, that is my router. It has issues, but I think the biggest one is the router (PC892). I would recommend one of the Chinese spindles and a vfd. Next up is lack of shielding of the linear rails - Ahren's carriages tend to compact the dust onto the 1018 CRS rails which can lead to stalling of the motors (or lots of time spent cleaning), so it would be better to protect them with some sort of enclosure. I have the Keling 425 motors on there which have lots of low end torque but drop off fast as speed increases. They really need more voltage than the G540 can handle, so I'd say that your choice of a smaller motor is good - it will have more torque at higher speeds. I'd also recommend going with the rack and pinion drive. It should give you a better force vs speed curve so you can cut faster. You'll also eliminate screw whipping problems which currently limit me to around 200ipm.

The best part of my machine is the mechanical structure, imo. It's pretty stiff. I plan on reusing a lot of the pieces for other machines after I get my new router going (still in the design phase). The one downside to my mechanical design is having the X rails below the work surface. This gives a longer moment arm from the gantry to the bearings so any force in the gantry applies a larger moment to the X bearings leading to higher deflection. It also tends to accumulate dust on the rails that flies off the table. So I'd recommend putting the X rails above the part and ditching the vertical legs of the gantry. There are good examples of that using Ahren's parts.