Eureka! (sort of ...)
Gave up on my blunted 60 degree blades, and I'm not sure why the new 45 degree blade didn't work so well -- a user error thing, I'm sure -- but I tried cutting again with a 45 degree Cricut blade. I've cut out some shapes and words on index card, and then tried the Georgia Pacific again, which worked beautifully at v100 and f60.
More experimenting to do for sure, but now I seem to be on the right track.
Thanks again!
Deborah