If you really need an i9 CPU, a desktop system is a better idea.  i9 CPUs in notebooks are known to throttle, being slower than i7 CPUs in equivalent systems. The screen type is whatever you're comfortable with - most will find 4K or QHD on a 15" or 17" screen uncomfortable for anything but viewing video.  If you really need that resolution, consider a large screen external monitor. If this is for professional use, a Precision workstation with pro/gold support is a better idea than an XPS.  
I'm very confused over i7 and i9 laptop. I'm video editor and graphic designer. So should I go with latest Intel Core i7 laptop or Intel Core i9 laptop. Also recommended the display type - Should I go with FHD, QHD, or 4K UHD. Suggest me the best dell laptop for my need. Provide i9 laptop deals and i7 laptop deals to save some. Thank you.
Should I go with i7 laptop or i9 laptop?