If you had the choice, would you get:
2013/14 XF-S Portolio with 3.0d
Or
2015/15 R-Sport with 2.0d?
The later one is the newer shape, is is significantly better? The 3.0 would give effortless power and be silky smooth. But wonder if the newer I4 in the latest shape would be sufficient.
Both are suitable replacements for a Merc.
I've not driven new XF (260), but have driven a small number of 250's, which are a great drivers car. The 260 has a better cabin, and is all ali construction. But a fair few on the forums say the earlier car drives better.
Presumable by XFS you mean the real 3.0d, not the half arsed one that most XF's get. Its a stonking engine, though the early 8 speed variants have gearbox reliability issues (much like the first of the 6 speed ones Jag used on S type, X types etc). Its smooth, quiet, refined and feels uninspiring... ...until you look at the speedo. But you're not one to use the engine much, so maybe the 4 pot tractor is more suited. Despite its low BHP, its torquey enough to be quite drivable.
The lower spec 3.0d is just pointless, unless you found your otherwise ideal car. Its same tax, insure and economy, and doesn't command much of a premium to buy. However, when I looked, most XFS Portfolios on autotrader turned out to be lower spec, even as low as Luxury.