I was in Katowice at the end of July and personally as a city I didn't think it was nearly as nice as Wroclaw or Warsaw but each to their own. To be honest I thought apart from the very center it was quite run down. However, for a GP it could work very well and the "Mariacka" is a very lively street with loads of outdoor bars etc. I didn't go in the Slaski but very impressive from the outside.