at 18x8, the most common aftermarket size, you could squeeze offset 42 in, as long as you stick to 225/40/18 tyres - these will fill the arches well and wont catch at the rear unless you lower the car more than 30mm from SE/standard
its difficult to get 45 or higher offset in the cheaper aftermarkets, but 45 might be slightly better. pcd is of course 112x5.
50+ offsets dont look quite as good anyway - they could do with spacers so you might as well get 42-46mm offset anyway.
i searched on ebay and found some rs6 style replicas with 46mm offset which is great, but i have 235/40/18 tyres so needed the extra clearance from a higher offset