You really could do it either way. Do what you think will make you more confident.
Doing your last long run 4 weeks before your marathon is doable. It's on the long end, but your body will still be ready.
Also, based on the info. you've given on your training pace and your goal time for the marathon, you could do your last long run 2 weeks before the marathon and be ok. 4 hours is somethig like a 9:05 pace so if you're training at 8:45 pace for 16 to 17 miles, a 2 week taper will likely leave you rested enough to meet that goal. It doesn't sound like you're trying to go "all out" which is a good idea for your first one.
If you do it this way, slow down for that last long training run - like 9:30 or 10:00 pace (or even slower).
Don't know what your other commitments are, but any chance you could take a day off work and put your long run at about the three week mark like you want rather than doing it on a weekend?
Post a reply on the Bulletin Board | Send email reply to Leif