Why not idulge yourself and buy the RS3, whack a good deposit down, have it on 24 months PCP but sell it after 12 months, the residuals are good so repayments low, done this a few times in the past and the loss in depreciation was minimal as long as you don't count the monthly PCP payments and just factor these in as fun rental!!. Audi will always want good quality PX cars that are nearly new for the forecourt and they market them at close to new prices so good for negotiation.
I'd run it for 12 months to scratch the itch then look at it again in 12 months time - phrase cake and eat it comes to mind.
I do like the RR sport but I also think that itch needs scratching otherwise false economy, personally I'd buy another Porker and run a small van or old estate for the dogs !!