So, let's assume you'll be doing 3 return flights LHR-CPT on SAA, 2 in business and 1 in economy. On top of that, 4 flights to Germany on LH in economy, and 2 flights to France on bmi in economy.

LHR-CPT is about 6,000 miles. Assume factor 2 for business and factor 1 for economy, that would be around 60,000 miles in a year. On top of that a few intra-Europe flights.

Enough to make it to BD Gold, but not enough for LH SEN. AC might be an option too to get *G. However, neither of those will be good for upgrading on SAA.

Just having a look at SAA Voyager. Doesn't seem attractive when flying business class, but quite good for economy class on SAA - 3 returns Europe-South Africa are enough for *G.

Nevertheless, I'd say that you are maybe best of with BD.

Edit: Maybe not. BD DC only gives factor 1.5 for business class on SAA. The search continues...

SmilingBoy.