Actually Glen, it depends. I've seen Korean monitors that are rated (a rated "overclock") for 60hz 4k and around 100hz at 1080P, lowering the resolution does put less load on the monitors components allowing for higher overclocks on the refresh rate.
But is is still just that, an overclock. Nothing guarantees that these 4k monitors will even reach 100-144hz at 1440P or whatever resolution lower than native.