If this is the spec on the model and you can buy for around £300 then I'd go for it. Then go to [Crucial] and upgrade the ram to 8 Gig to cope with Windows 10. Keep the Dell as backup although I think the battery will need to be replaced or removed altogether. Keeping a dud battery in a laptop is a recipe for disaster.
Surface Pro 5 News - release date, UK price, features, specs