How should I adjust my half marathon goal?

Go for 10 miles at 7:16/mi. If you still have juice in your legs, kick hard for the last 5K. If not, hold on the same pace for dear life. Jack Daniels puts 20:21 around 1:33 HM, 7:16 is around 1:35 HM, so it would be stupid to still target 1:40.

You should be able to go a little faster than the 10 @ 7:16/mile. You probably shouldn't be able to do much more than 6-7 continuous @ HMP in a normal week of training without feeling wrecked. Sub-1:35 should be the goal. 7:05-7:10 or so. Maybe start there (7:10) & stay there through 10k. Then try to run as many 7:0x miles as you can to the finish.

When I was first getting into it, I ran 19:30 (late fall) & 1:30:00 (early spring) pretty close together. Ran sub-19 & 39-flat a couple months later (late spring). Was making some progress just upping the mileage like you were. Ended up running 1:20/2:53 in the fall. So pretty much a year to go from 19:30/1:30 to 1:20/2:53. Just started running a lot.