Which wheels?

This is interesting....especially that Steve Hed will not build carbon wheels for rim-brakes....

https://cyclingtips.com/2017/12/carbon-clincher-safety/

Carbon is a poor heat conductor (vs alloy) and whilst carbon is a strong material - it is held in place with resin and that resin quality is paramount.... 

In me personal experience rim brake carbon wheels stop as well as alloy wheels in the dry. Just make sure they're set up properly, for example toe in the pads correctly.

When it's pouring down they take a bit longer to start braking than alloy rims but like you, I only use my carbon wheels in the dry.  If it's drizzling or only light rain then there's no difference.

TBH when it's pouring down all rim braking is pretty sketchy and this is when disc brakes come into their own. 

I agree about using the correct pads, Swiss Stop Black Prince are very good but pricey, I find the blue Wiggle Lifeline ones are great (rebadged Reynolds pads) and cost only a fiver for 4. 

In terms of wheels, I had mine built by Wheelsmith and they've been excellent and cost no more than from someone like Hunt.

I'd personally always choose a wheelbuilder over a brand and aside from Wheelsmith I can also recommend DCR Wheels and The Cycle Clinic.  

I'd be a bit wary of the reviews given on carbon rim braking in the wet.  I have some Black Inc. wheels on my Factor 02 and, despite several good reviews for wet braking, having tried it once I will not be doing it again - even on the recommended Swiss Stop pads.

The alloys will give you more flexibility and are probably not much heavier, if at all.  Indeed, you have to spend a lot of money to get sub-1500g carbon wheels whereas some hand-made Open Pro USTs or Kinlins (which Hunt use) can be had for GPB 300ish

Planet x are selling Campag Zondas for £300 which is a steal

i also looked at the Hunt wheels but there was a 8 week wait and they were £60 more. No contest... tey're mnow on my bike and loving them. They'll be a huge step up from your current wheels

I have a pair of Easton EA90 wheels I use in Winter while my Summer wheels are the Prime PR38's, so I do have a benchmark for alloy vs carbon. I use Swissstop Flash Pro Black on the alloy rims and Swissstop Flash Pro Black Prince on the carbon rims. In both dry and wet conditions and on both alloy and carbon rims my braking performance is sufficient to lift my rear wheel, that's about as good as you need it.

I find that I get a little smoother modulation on the alloy rims while the carbons are just a bit grabbier especially in the dry. In the wet they are both much the same. However it was not always thus. When I first got the carbon rims I used the pads that came with them. These were OK in the dry but very scary in the wet so I switched to the then top Swissstop pads for carbon, the Flash Pro Yellow which I will admit looked a bit trick. These gave a much better performance in the wet and when they wore out I opted for the newer Black Prince compound. These put the braking on my carbon rims on a par with my alloy braking.

So what I am suggesting is that braking performance of alloy vs carbon rims is, thanks to Swissstop, no longer an issue. Certainly give the pads that will come with your shiny new carbon rims a try, just remember to give them lots of anticipation in the wet and be reassured that there is better out there.