Thank you so much for giving such an indepth answer. I had read your article about the best specs, so I applied that when choosing, and I went for models specifically with the RTX3070 graphics card and Intel i7. All the machines on offer have only 16GB RAM - 2x 8GB, 4 slots, and configuration for 32GB doesn't include any 8GB chips, which is pretty rude of Dell.
Thanks for the tip on the power supply - I'll add that to my list, as I didn't realise it made a difference.
I had ruled out the Alienware as overkill, but there is one with comparable specs (i7 11700F, 16GB RAM (XMP a bit faster), 3070 graphics card, 512gb SSD [smaller], 1TB HDD) to the XPS on special - $3,000 ($1,000 off) compared to the $3,200 for the XPS. When I realised there could be overheating problems in the G5, I looked again at the Alienware and discovered the one on special has super-duper liquid cooling. I'm not sure if that's overkill, given that it's not for gaming. And it's ugly.
Yes, I'd like it to last at least 5 years. Perhaps I should wait a while and see if a suitable XPS comes up discounted. There are so many sales and discounts these days, I wonder if full retail prices are inflated. I don't think we'll be going back to pre-COVID prices in a hurry.