Raster can render at 4K while RT renders 1080p + ML SS.You DO know that 4k@60fps is an insane increase of pixel and data over 1080p@45 and therefore it is really "silly" to easily say it "should be possible" with some tweaks right? it's at least 4 times as many pixels and then a whopping increase in fps. At that resolution you'll need serious power. power that won't be available this coming generation.
it's like saying that a car that goes about 200km/h would go 800km/h with "some" tweaks.
no car can drive 800 without a rocket engine screwed on top