Originally Posted by veroniquem
By the way, Fed won Basel 3 times as a 250 and twice as a 500. It makes a difference imo as it's not the same level of competition.
Not really. Under the 2000-2008 ranking system Basel was an International Series Gold tournament. Those tournaments were effectively the precursor to the 500 events, which were introduced from 2009 when the new ranking system was implemented. Tournament ranking points were pretty much doubled across the board from 2009.
International series gold tournaments awarding 250 points to the winner from 2000-2008 (apart from Dubai and Barcelona which awarded 300), then all doubled that to 500 points from 2009 provided they weren't demoted in status.
So when Federer won his Basel titles from 2006-2008, the tournament had effectively the same status/tier as it did from 2009 onwards.