I have SSL suspension up front and matching Bilsteins at the rear on my 2011 +4, oh! Mulberry BRBs as well. I had the car fitted with SSL suspension when i bought it so i dont know what the standard set up was like. However, i can say that the biggest improvement i made was to thoroughly lubricate the cart, oops sorry, leaf springs with a cocktail of SAE 90 and SAE 140 and i do this every year whilst the car's in hibernation. I've had the car 7 years, when i first oiled the springs it appeared that they had never been lubricated from new so I'm not sure what they used to do at the factory.
I also had the seat sqabs repacked with better quality material and suspension rubber and made the squab angle adjustable in order to support the thighs
