Dane, I can help. I have a first-run Sweet 16 head, and a rev C combo. PRS uses a Celestion G12H in the combo, and a Celestion Vintage 30 in their Big Mouth 1x12 closed back cab. I've run both amps through both speakers, comparing the amps themselves. I've plugged the amps into other cabs, too.
Celestion G12H in open back combo. Not best for clean with either amp. I think the box is too small.
GWS speaker in a Bugs Dallas amp. Higher wattage speaker didn't help me much keeping it full. Clean, yes. Full, no.
Celestion Vintage 30 in PRS large 1x12 closed back cab. Better, especially on the bass side of things. Really good going into "grit".
Celestion Heritage G12 in Marshall JTMC12 1x12 open back cab. Better still. Cab is close in size to PRS above. I think a large, open back cabinet has a better atmosphere with clean guitar sounds. Not as good for "grit".
Jensen C12N in large 1x12 open back Fender cabinet. Best of the lot for clean. Big, round bass. It was the deepest cabinet by an inch, or so.
I also ran it through a Mesa 2x12 closed back cab. Don't know what speakers were in it, but it weighed a freakin' ton. Only slightly better than the 1x12 closed back for clean. Best of the lot when cranked.
So, my conclusion in all of this is that a larger, open back cabinet fared better for clean tones. A higher wattage speaker didn't help me much with "this" amp. Any of the Celestions would be a good choice. I think a Celestion G12H would be good in a larger, open back cab.
The guitar's volume knob makes all the difference with keeping a Sweet 16 in the clean zone.