some people anger with grade 18's o.O
...that's not me, but yeah, you can do that if you're chasing the 10 trill scores etc.
...I don't use mouse recorder, but I tend to alternate angering with grade 6-9 (my junk gems, for angering swarms), grade 11-13 (armored waves especially), and angering with grade 14's and 15's, with the occasional 16 (giants only).
two grade 7's will get you more score than a grade 8, but you will have more hp to deal with, and a slightly higher armor.
however, if you were angering with, say, 10 grade 7's, you would (i think) get slightly more score angering with one grade 8, followed by 8 grade 7's...but the monsters would definitely have a lower total hp. 2 grade 8's and 6 grade 7's would start getting less (I think. It's been so long since i've seen the actual formula...)
In general, just toss junk gems (grade 6-9)at swarms, grades 10-12 at normal, grade 11-13 at armored, and grade 14+ at giants-provided you've gotten started.
as for what hp to target...I think you've just about got it right, though go for much less with swarms/runners, and way more with giants, and somewhat more with armored. alternatively, use a single super-slowing trap (or a bunch of r/o/b traps), to get lots of over-angered monsters, and then don't anger much for a while as you kill the toughies.