If you mean effeciency in terms of time, i *think* that colder water would reduce the pore size of the RO membrane and reduce your output rate in addition to reducing the pure/waste ratio. I don't think it should affect resin consumption, because the water coming out of the RO should be of the same quality, it just gets there slower. As for pressure, i believe that higher pressure is better (i.e., it pushes water through the membrane faster), but that you get a diminishing return after what you would expect your max household water pressure to be (something like 80 psi is where the charts start to drop off). You have other things that will fail on your unit (fittings) before you can go too terribly high, and you don't gain anything from doing so.