To LUXURY1...Personally I've owned 29 sports & or GT cars over the years. Actually, I've never been without a 2 seater in my possession since I got my drivers license at 16. But I've never had the pleasure of owning a Porsche or a Bimmer. From what I've read, the cars that you are looking at are distinctively different machines from the XF. Each with its own merits, and its own drawbacks. You really can't go wrong with any one you pick. I can tell you this much, in the 6 mos. and 6K miles that I've had my 04' XF, 6 speed, I have never once regretted buying it. And when compared to the nearly 100 other cars I've owned in the last 37 yrs. the XF ranks as the nicest ones I can remember. (and I remember them all).
Truthfully, I haven't driven my 96' Viper GTS or my 91' Miata since my XF purchase. (I don't know if that says more about me or the Crossfire.) I've only had my 69' AMX out twice.

To KMAG50...As for changing oil, it really isn't that hard to drain the oil from underneath. Just 4 bolts hold the cover that hides the underside of the engine. I use a small $20 floor jack I purchased at AutoZone to lift it. I also bought the oil filter socket there. (Don't forget jack stands). The filter is almost a delight to change, especially when compared to any other filters. (just make sure you get all the O-rings in the right position.) I did have to go to a MB dealer to get a factory filter (only kind I use) because the closest Chrysler dealer to my house told me he didn't have any in stock, and never did! (another story) Anyway, Mobil 1 from Wal-Mart, and factory filter comes to around $50.00. If you still want to try the dip stick changing method, try a boating supply store, or a boating supply catalog to find it.
To answer the oil question, I've used nothing but Synthetic for the last 26 years. "I highly recommend it". Especially if you like to keep your cars for a very long time like I do. Since Chrysler recommends Mobil 1 that's what I use in my XF and Viper. But personally, I think you can't go wrong with any popular synthetic. Just make sure it's the correct viscosity recommended.

To PUNKIN...Very eloquent, very eloquent indeed!