I'm struggling with the same dilemma at the moment but at the 15" size point.
I just bought the XPS 15 (2020 model) in the i7-10750H / 16 GB / 1 TB / 4K touchscreen configuration, with 4 years of extended warranty, and it set me back $3000 USD here in the UK. This was with 16% Dell Advantage discount. For comparison in the US a slightly better package with 32GB of RAM is currently up for less ($2,750, so more like $2,900 after sales tax I guess). Retail.
I've also bought the exact same configuration and package, refurbished from the Dell Outlet, in the standard HD resolution for $1,900. This one has yet to arrive.
So how does the 4K XPS fair in Linux?
I booted in to Ubuntu 20.10 using a USB stick and... the keyboard didn't work. For some reason Ubuntu brings up the on-screen keyboard when I use the touchscreen, but the physical keyboard is completely non-functional.
Fedora 33 live? No wifi.
Manjaro XFCE worked great. I was pleasantly surprised (once all the 4K related scaling settings were fixed) how good it looked and how well everything just worked.
Paying $1,100 for a 4K touchscreen upgrade that causes nothing but problems on Linux is a hard thing to justify and, unfortunately for Dell, the screen on the XPS is probably its biggest selling point right now. Now M1 is a known quantity they really need to discount these laptops imho.
On the XPS you only get 3 USB-C ports, and one is constantly in use for me because I rarely unplug. I will be needing a stupidly expensive dock, so I have no idea how anyone can cope with just the 2 on the XPS 13. The keyboard is better than average but still pretty harsh, the touchpad has borderline build quality (springboardy) and is too large for my tastes (and I miss physical buttons), and the although the screen is gorgeously sharp and bright the fact that it's glossy still causes reflections in my home office.
I do not think I will be keeping either laptop, and instead I'm looking toward the X1 Extreme Gen3, with its better port options, keyboard and build quality.