If I havent given enough information sorry you can just ask
It's your money, your decision. We all have our own ideas for what you should do and i don't think any are really wrong
1) if you want the fastest now then go the 5800x3d/b550/32gb ddr4 route. It'll give you what you want but you're on an end of life platform and this is as good as it'll get...want to upgrade, you need new everything(mobo/cpu/ram)
2) go with a 7600x/b650/32gb ddr5 route. you will be slightly behind in fortnite but still get close 450+fps av at 1080p(1% lows still above 200fps)so it'll max out a 240hz monitor. Current gen platform and you'll be able to drop a later gen cpu in without having to change your mobo or ram(that's quite a saving n my book). 7600x on a par really with 5800x3d..50 game av below(they have 50 game av 5800x3d 4% slower at 1080p, but fornite likes the vcache, so that one's faster)
We take fan favorite Ryzen 7 5800X3D and compare it head to head with the new Ryzen 5 7600X in over 50 games. Yes, the 5800X3D is...
www.techspot.com
if you can find a 2nd hand 7700 or 7700x for £200, get that as it on a par with 5800x3d for fortnite(though vid is 1080 epic quality 4min43)
7700x works out 10% faster than the 5800x3d on 42 game av, though forniter not in there
3)if you don't mind either way and don't plan any upgrades, get whichever one is the cheapest that you can find
Are you ever going to play some other games..only asking as for several years my son just played fornite, which is fair enough...then all of a sudden he stopped (still goes back occasionally) but now he plays way more, and not just online shooters but single player games also. Think his friends starting playing other stuff too, and online gaming is more social as well, so they all just naturally started trying different games... for some strange reason he likes to go around and complete them all in epic hard mode or whatever(single player that is)...anyway, if you think you'll branch out, I'd go am5
In q1 this year(jan/feb/mar) AM5 overtook AM4 as the number 1 build now for amd as prices had dropped enough for new builds that people naturally went am5 over am4 now...that'll only accelerate I think, and as am5 becomes more dominant and am4 declines, you'll get more am5 parts 2nd hand and am4 parts wmanufacturing will decline also...personally, I'd only go am4 for budget build now...something I'm actually doing for my nephew, but I'm limiting cpu/mobo/ram to £200(so 5600x/b550/32gb ram...should get it for less atm with patience)...that way upgrade in future wont hurt as much