[Vwdiesel] LubriMoly Synth vs: Dino Oil

[Gerry]

My local VW maintenance/repair shop has been using Castrol oil (I think it's "RT") for diesel applications -- 15w40 with CH-4 rating (relatively cheap).  They're now switching to LubriMoly synthetic, 5w50, with a CF diesel rating (expensive).

I use either Rotella 15w40 CH-4 or the Castrol 15w40 CH-4 in summer and Delvac synth 5w40 in winter (ridiculously expensive and almost unobtainable here in Toronto).

Is CH-4 "better" than CF?  If so, would the synth vs: dino offset this?

Which is "better" for summer -- 5w40 or 15w40?

My application is a '91 Jetta TD (requires CD level).  I change oil every 5K km and always use Mann or Mahle filters. After 240K km, the engine uses less than 0.5litre per change.  I'm doing mostly city driving, with occassional longish highway trips -- always well above the posted level so I don't slow down the rest of the traffic... :-)

I'm sure either of these diesel-specific oils is adequate, but nothing is too good for my "baby".

TIA for comments,
G.