Sorry, should have been clearer, just wanted the tax amount. Have 50 something thousand miles and a few thousand sitting in an SPG account that I'm going to transfer. Was wanting to know if it was worth it, and it seems so!
I did try to do a revenue booking using multi city but it wouldn't let me route the same way, I assume because there are revenue seats on BA still available so it was suggesting EZE-GRU-LHR-MAD-LHR all on BA rather than EZE-GRU wth BA, GRU-MAD with IB and MAD-LHR on BA.