Granularity of node panes

I'm on Panels 3, and from what I can see, one can use an individual field or an entire node as a panel pane. I've just built a simple module that uses the Field UI and field_group module (or is it fieldgroup?) to float an image within a bit of text. I was thinking of digging into content_type and building something for field groups that would provide some intermediate granularity between a field pane and a node pane. I'm relatively new to panels, though, so I wanted to be sure that this facility doesn't already exist. I noticed that one of the reservations against using field panes was the expense of seperate rendering calls for each field: wouldn't such a module mitigate this reservation?