Ok, it seems that only too much is enough for me.
I've been looking at Sigma/Tamron/Canon 1.4x TC's for my Bigmos to expand the reach even further! Is there something I should know about them and their compatibility or are they pretty much the same? I'm leaning towards the Sigma because the other ones are white and look silly with a black lens.
Edit: Oh damn, there's a sticky right above my post... How do I always miss these things?