Glad this old thread is still kicking! And I can't agree more with what SMP said. My main machine is a mechanical Bernina 1008 and it does garment weight leather just fine. Anything more and I need to get on an industrial with a teflon foot. If it's fairly thick, or many layers of anything heavier, I opt for the industrial walking foot. It just depends on what you want to work with.
Right on! It also depends on the quality of the leather. Since it's natural hide, not manufactured, there are going to be thickness variances in a single piece regardless of the oz. A walking foot can help if you get a really weird piece that's "lumpy".