I hate to be a purist, but Cabernet is not Port. It may be made in a Port style, but it doesn't taste the same. Real Oporto is made from Touriga Nacional grapes. In Portugal. And preferably by Taylor Fladgate, Cockburn, or Dow. A little bit goes a long way, so you might as well get the best stuff going. Vintage Port is a bit of a bother to keep, open, decant, and serve (you wouldn't believe the sediment it throws), but it is unbelievably good.
You're quite right, of course: Pindar's Cabernet Port does taste different, and it's quite heavy. My staple is Dow's tawny. My favorite vintage is 1977, opened only when I know we'll kill the bottle.
Cheers! : )