After reserving two 200P GFN19 ranges and finding out they'd take 24 hours each on my GTX1080's, I've bumped up the maximum reservation size from 200P to 400P. If you can finish that large a range in less than two weeks, feel free to reserve one that size. If you cannot, please choose a shorter reservation.
And remember, this is manual sieving. Don't go making a reservation and thinking that BOINC will magically run it for you. This is entirely separate from our BOINC subprojects and involves downloading programs (and sieve files for Factorial or Primorial), running a program from the command line, then uploading the resulting file back to PrimeGrid. Not a week goes by that I don't ban people from manual sieving because they make reservations and then completely ignore them in spite of a reminder PM from me.