I should add that even if you're not happy with an upscale from 1000x1250 to 2400x3000, you'll almost certainly be satisfied with a compromise. Even a render at 1700x2125 is going to be about 1/2 the pixels (edit: i.e. half the pixels of 2400x3000) and therefore not much more than half the render time, and I doubt you'll be able to tell that you've enlarged it, quality-wise.

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Hardware: AMD Ryzen 9 3900X/MSI MAG570 Tomahawk X570/Zotac Geforce GTX 1650 Super 4GB/32GB OLOy RAM

Software: Windows 10 Professional/Poser Pro 11/Photoshop/Postworkshop 3