I attended a concours clinic not long ago held by Chicago PCA. One of the national judges and competitors showed us a mixture of "3M hand glaze" and a dab of "Blue Magic" ...this stuff polished the rear window of a volunteer's Boxster to complete clarity. I now use it on mine and the results are superb. Follow up with a coat of "Plexus" and you're good to go.
I like the Novus system on my rear window, removes micro scratches & abrasions. If your scratch can catch a finger nail, you might be looking for a new window though.
I'm finding that Plexus is more like a wax. It fills in the gaps and scratches, but wears off after a month or two and you have to use it repeatedly.
Stuff works like magic though! I'm sold on using it until I can trash my crappy plastic window top and get a GAHH glass replacement top at the end of the year.