My opinion the design looks great on Asus, as durability and quality Dell is more durable, but as performance they might look the same but the I7 8550U is better than I7 7500U. Here u have a comparison on them maybe will help u a little.
Both are gaming both have the identical specs even the memory only difference is the HDD, i would go for Omen for the price first and for the hard drive. In my opinion you won't have heat problem with neither of them because both are meant for Gaming so both have extra colling inside.
You won't find a new one, only if u find a broken laptop same model and the motherboard is working and u will replace it, but first find if the CPU can be switched to the other board because there are laptops where u can change the CPU and there are where u can't replace them, or try finding one...
I would go for HP pavilion, 1 inch bigger display, and dedicated graphics card gtx1050ti even if is an older gen, 7700HQ is still very competent, and Asus i saw has only an SSD of 512GB and the HP pavilion have a 1 tb normal HDD and an 120gb SSD.
Unfortunately you can play only old titles of Call of Duty and games older than 2004 - 2005, the video card does not help you that much neither the CPU.