Hi Dave,
I will try to answer your questions on the ARC17.
The ARC17 is the same boat, hulls, mast etc., as the SC17 with rigging upgrades.
The boat is 8.5ft wide. PN adj = 0.995
It has a square top mainsail. PN adj = 0.980
The self tacking is smaller in area than the old SC17 jib. No PN adj. factor?
Does a 1.005 factor apply?
It has a spinnaker with launcher and retraction system.
PN adj = 0/.960
This is the boat with all the bells and whistles.

Therefore the adjusted PN = .960 x 0.98 x 0.995 x 0.73 =
0.68335 for two persons sailing the boat.
For single handing add the 0.974 factor and the PN is 0.66558.
Since the same boat is sold as a one person or two person boat, sailing it either way is well within class rules.
As far as the difference in boat feel goes, there should be very little. The boats are the same width so the roll inertias are very similar and the quickness that the boats fly a hull will be very similar. Fore and aft the boats will feel similar because even though the 17 is shorter it has taller bows, which tend to restore the pitch inertia lost due to the shorter hulls. Also the 17 has clean, elliptical topsides, decks, that will split the water just as easy as the keel. Therefore you don't get the "slam on the brakes effect" when you drive the bow under. The boat recovers really sweetly.
Look at the one picture of the SC20TR in the Steeple Chase Race in Cat Sailor. The leeward foredeck is underwater. Are the sailors in that picture diving for the rear beam? No, there is no problem and no reason for alarm on this hull design. The elliptical foredeck splits the water easily and this boat just keeps right on ripping. Another hull design would be doing a forward cartwheel in this same situation.
Good Sailing,
Bill