I picked up the GS645 a couple years ago and thoroughly enjoyed it until replacing it with the GF670.
The S and W versions are more fragile when in the bag whereas the 645 is a folder and thus very safe when closed up. When in use you do have to be careful with the bellows. And if you get one with the original bellows, chances are you'll have to replace them at some point. But I'm pretty sure the one I bought had new bellows because they were in very good condition. I've read that the replacements are far more durable than the original bellows because better material is used.
The native portrait orientation takes some getting used to, but if you are committed it is very easy to master. You mentioned not needing a meter but I found the built in meter quite accurate and very handy. You can read more of my thoughts on this camera here. http://chemicalcameras.wordpress.com...-professional/