My credit score across all 3 bureaus is 780+. Not sure about you, but I’ve worked too hard (over 20 years) to build up my credit to where it is at today.
The A6 is a fun car. It is a 6 cylinder with about 335 hp. It is a bigger/heavier car compared to the A4, but when I put my foot down on the accelerator it moves. Gas mileage has been good on the highway. I get over 30 mpg. City driving is in the low 20s, but I am okay with that.
S4 and S5 is going to cost you. Same with the E class since deals were not that great pre-covid. You could get a decent deal on a 5 series through brokers on this site. I would forget about the A6 at the moment since discount off MSRP is not that great, and not much in incentives are being offered.
My advice is keep the A4 for at least another year or until the market improves. Check out broker deals in the Marketplace.
For reference, here is my deal from last year on my 2021 A6. I plan to keep the car till lease end and either get into the A6 e-tron (if deals are available then) or something else. I have no brand loyalty.