The 280CDi delivers equivalent bhp to the old 210 3.2CDi, so more or less the same in performance, I'd certainly be happy with one. Both are based on the same engine so very easy to tune by chipping/remapping. If it was the ML I'd go for the bigger engine. .
Unless you do a lot of rushing around on single carriageway roads, with lots of marginal overtaking, I doubt if you will notice much difference. The 280, as has been said, is pretty much on a par with earlier 320s, and they are very capable motor cars.