I'm surprised that your HP5+ negs appear thin when developed in ABC for around 8 minutes. I pull mine at that time as well, and they are more on the side of dense than thin. I rate my film at 320 but expose for my ZoneIV. My developer has a temp of 70°.
On normal VC enlarging paper, I use between grade 2 and 3 to get a good print when developed in PMK, BUT with ABC, between grade 0.5 and 1.