Heh, it only took me a week to take your advice and buy this one
A bit of further research turned up a couple of interesting factors - firstly the notebookcheck benchmarks that put the Radeon 530 level with a 940MX DDR3 were done with a
DDR3 Radeon 530 (according to their listings, at least) so I'm hopeful that a DDR5 version will perform better; and more importantly the base laptop can be configured with dual storage and it appears that the M.2 slot will be available and unpopulated in the shipping laptop, leaving the possibility open that I can add an SSD. It's also possible that the laptop will ship with single channel RAM despite having two RAM slots (the 8GB versoins on the Dell website do*), which would open up the chance to expand to 16GB in the future.
I'm very lucky to have a couple of wonderful people who helped stretch my budget for my birthday
* however, the ones on the Dell website also only ship with an optical drive (this one doesn't), and there's no option for a 1TB HDD and a dGPU. So goodness knows what will actually turn up