2) "Any other "indicator" workouts to give me a sense of whether I should trek out at 6:00 pace come 10/10/10?"
FWIW, I really didn't care what you were attempting to run the New Haven race in. FYI, I have run NH a few times and it is very difficult to predict a time there as it can be very hot and sometimes humid.
I was addressing your second question noted above. Run 20 at 6mp (and I'm not the only one to suggest you do 18-20 at marathon pace)and, as I said, you will be mentally and physically ready to achieve your goal.
The other factor in doing this is it's your first marathon so pacing is essential.
Sure, the pacing within long runs are great but it's not 20 at 6.
Just my .02 cents.
All the best,
TPM