I don’t think £500 + your 1080Ti will get you a 3080Ti. Gonna need a second pot.I'm the same. I have a little savings pot and there's been money for a new GPU in there since around August 2018! A nice round £500 and I'll add whatever my 1080ti sells for.
Is double the performance a reasonable expectation when going 1080ti to 3080ti? It can't be far off, surely?