Have you had a shot in a 5 Series rather than an A6? You might be surprised. My older 5 Series had an amazing ability to feel stable at a cruise while still being amazingly fun and agile on twisty roads when required. Coming from Imprezas and an old VW Corrado for reference as knowing what a decent twisty road car handles like.
It's a crap cliche I know, but 5 series shrink around you. I've driven a number of 5 series through the ranges E34, E39 and E60 (though not an F10 yet), and owned a couple too. Though they're physically quite a big car, they always handle far better than they have any right to, and feel more like a 3 series to drive than you would imagine.
5 series also depreciate a lot faster than 3 series, so you can buy a lot more car for your money 2nd hand.
I feel the age related thing for your "company car" is a bit crap though, given they only give you an allowance per month rather than giving you a car to drive. Have known a couple of people get jobs like this, get told they must go out and get a car that's under 5 years old for a mere £300 per month, then 3 months later they've been made redundant and the £10k car they just bought is worth £7500 now if they're lucky! A bit of spit and polish, a £250 private plate, and would anyone know your Golf is as old as it is unless they looked at the V5?