Help me spend some money

All depends on how nerdy you want to get, if you want to go full on then I would look at the route, define how fast you want to do it, then calculate the FTP (and therefore percentage thereof) that would be required to hit your time with the 11kg current bike, a 9kg example, and then a 7.5kg bike. I'd just pick the climbs to make this a lot easier to work out, with maybe an overall target of (say) 180watts average for the whole thing as an indicator of total pace.

Then you need to look at what it'll take to hit each weight for the bike - buying Dov's bike is likely to be the cheapest method btw, or that Rose, but dropping the Donhou is more challenging.

I'm going to guesstimate that the fork is 750-850g, so that's the first place to drop weight - ENVE 1.0 is 295g so that's around half a kilo off the front end.

I've got an R1 Arione that you can have for the price of picking it up which will drop 75g off the saddle, so we're at almost .6kg already.

The wheels show a lot of promise as an area to drop weight, as is the group - but now you're really starting to get into the serious money realm.

Record is £1,030 from Ribble, that'll drop a decent chunk of weight, crankset and cassette mainly I'd guess but the whole system will be lighter.

Wheel-wise it's shallow profile carbon tubs time, Zipp 202's would be 1,180g which is going to take nearly a kilo off the wheels I'd (wildly) guess.

That's a further £1,500 for the wheelset, plus a decent pair of tubs (I've some Schwalbe One's you can have for this project to help you along).

Then you need to look at each item in turn - what are the bars, alloy? Change out for carbon ~£300.

Bottle cages - King Ti drop some weight but don't compromise function, that's a further £100.

Etc etc.