Yes, drive sprocket = rim. As for the chain, I don't think that chip clearance is going to be an issue when felling or bucking with a 28" bar. The 660 has the power to pull that length in full comp chain and to clear chips, cross-cutting or ripping. I've cut and bucked hardwood and softwood with my former 066, and was never wanting for power or chip clearance with a 28" bar. With a 36" and skip, I was fine, too.
The only time I'd be concerned about problems with chip clearance would be with long bars like 42"+; 36" requires awareness and prefers skip, but proper technique with full comp (cut, clear, cut, clear) will produce good results and safe, predictable felling cuts. With the big bars, chip clearance becomes a problem and a slack chain can permit chips to wedge between the chain and the bar, jamming it up and creating all sorts of annoyance when bucking and potential danger when felling. I'm talking about full-bar work with a 60" bar in this particular case; I have never had any problems with the 42" setup, even with a slack chain.
28/skip is the right combo for a Stihl 440/441/460 and other 5-6hp saws. My Dolmar is right on the cusp, and can pull full-comp or skip with a 7t sprocket. Skip has been great in cottonwood and willow, where the chips are huge and chip clearance matters more. In hardwood and "tighter" softwood, full-comp gets the most out of the saw. The norway spruce pictured was felled and blocked with Stihl RSLK (full comp, square ground), and you could lean on the saw a fair bit and still stay in the powerband. The same combo, with the 066, could have been leaned on really hard without losing revs, and would benefit from lower rakers and/or an 8t sprocket. The Stihl 076/42" pictures were of willow (felling) and maple (shown blocking), and chip clearance started to be an issue a couple times when blocking through crotches, where the competing grain direction made funny-shaped chips that needed the room that skip provides to be pulled out smoothly.