These are the "rated" flow specs (flow is what you want, not pressure) -
Karcher -
1.3 GPM
AR -
1.1 GPM
I would be looking closer at the Karcher in that case. You could also boost that flow by opening up the nozzle orifice.
But, I think either of those would be pretty cumbersome wall mounted. I'm not sure of the arrangement, but if you can, take a look at the K3 Horizontal (1.45 GPM) or Cube 1800 (1.2 GPM). Both are similar in price to the one you are looking at, and the Cube has standard threaded connections which makes it easier to upgrade to a longer/better hose in the future. Both would be a much better wall mount solution and don't end up paying for useless crap you don't need. If it were me, I'd be looking at the K3 Horizontal for the higher flow rate.
The K 3 Horizontal FJ pressure washer is our smallest K 3 model. It is ideal for cleaning dirt from patios, garden furniture and cars. Includes our popular Foam Jet nozzle.
www.kaercher.com
The Performance Series K1800PS CUBE™ offers high cleaning performance and unparalleled ease of use. This electric pressure washer delivers 1800 PSI of TruPressure™, ensuring you get the highest level of cleaning power.
www.kaercher.com
Reach out if you need, I'm happy to help get you on the right track.