Your CPU is probably holding you back in situations where are the more cars on the track. The 5700 isn't bad, it's definitely not worth keeping long term though. In the current climate, there is no real good value systems to get the most out of the G2. I think you will be waiting until February before there is any significant stock available of anything. So, I wouldn't buy now if I could possibly hold off a couple of months. Waiting as another advantage, the 3080Ti will be out by then and it will be another option to consider.
however, you might not want to wait. If so, join some of the discords that are keeping an eye on stock levels and you might get lucky. My recommendations are as follows
CPU: AMD 5800x.
GPU: Nvidia RTX 3080.
If you get a 5600X and an RTX 3070, you will still have a great experience on the G2. But, if you aren't likely to upgrade for a few years, I would get the best I could within my budget.
You will need to upgrade your motherboard, ram, psu etc. Suggest you get a minimum of 32GB of Ram.
And, yeah, you are right, it ain't going to be cheap!! No matter which option you go for it's still going to be above £1500. If you can get one of the Nvidia Founder edition cards, that will save you a bit of money.