Not sure where your getting the +30% and +60% numbers from unless you mean raytracing? In raster though the 4080 12gb will only end up around 15% faster than a 3080 at 4K while the 16gb will be around 40% faster.$700 to $1200 is 70% – that's one way to look at it. Also, what you're doing there is comparing the lowest-spec 3080 with the highest-spec 4080. The right comparison is 3080 10GB versus 4080 12GB (£649 versus £849 – 30% increase), and 3080 12GB versus 4080 16GB (£749 versus £1199 – 60% increase). There are lots of ways of slicing it, but the most dishonest way is to claim the 4080 is 'twice as expensive' as the 3080. It really isn't, so repeating that it is isn't helpful, it's just rhetoric designed to make people angry.
I'm not going to say the pricing of the 4080s isn't ridiculous. It absolutely is, and no one should buy one in an ideal world! But twice the price is a stretch too far, and unhelpful to the conversation.
The FE is the cheapest card and the 3080FE is £649 the 4080 16gb is £1269 which is a 95.6% increase for uk buyers. The 4080 12gb doesn't even have an FE card so even though pricing starts at £900 it's unlikely that any cards will be available for £900.
People should be angry, nvidia is trying to rip us off. They spent the past 2 years prioritising crypto miners over gamers and now the miners have ditched them with a load of stock they expect gamers to pick up the tab.