We hit a big old GS at around 4 months too. I say around because they hit the spurt when THEY hit the spurt; not necessarily bang on 4 months. And a stream of GS isn't too uncommon. For us, the first few months were GS crazy, then monthly for 3 & 4months, 6 month and the mother of all GS at 9 months. It lasted on and off a whole month.
Best thing for a GS, IMO, is to go with demand. Because it's natures way of setting everything up to run in sync. Follow the cues (like Elena's Mummy posted make sure it's genuine hunger cues) as he knows how hungry he is and how much his body currently needs better than we do. If you follow his cues, it should pass over a few days to 5 days or so. It can last longer. It can be done and dusted within 48h! It depends on your babe and what their body is telling them they need. But if you follow cues, your supply will adjust faster and thereby, supply meets his demand.
At around this time, Mamas who are single side feeding find they need to move to double side at each feed. And the duration of the feeds isn't anything to worry about too much - they get more efficient with time. Just watch for the sucking and swallowing, plenty of wet and pooey nappies, content baby. If you think he isn't finishing the breast at a feed, test to see if there's still plenty of milk left in the breast after the feed.
Ummm, what else? Not all babes are the same. They grown at different rates, their tummies are different sizes and just like you and me, they have different appetites. Mamas don't all produce the same amount of milk either. So, while it might seem like all babes should be able to go 4 hr between feeds at 4 months.... well, it's kind of like all of us should be able to go the exact same amount of time between meals. And if we're getting different sized meals, well, that's no fair!
Lots of Mamas here weren't on 4EASY until 6 months - they worked the EASY around their babes, following the structure and tweaking (babywhispering) to what their babes were telling them they wanted and needed.
Looking at your EASY, I do wonder if there's a chance that it's not just a GS at play here. The OT naps (usually 30min nap is considered OT) is followed with a long A time (Awake = eyes open to eyes closed, include E in the A time). If you can, cut the A time right now after a 30min nap so it's literally (at this age) a nappy change, feed, nappy change, loving gazes and off to bed. Also, if you're getting much crying while trying to resettle this will be a real calorie burner, leaving LO hungrier.
http://babywhispererforums.com/index.php?topic=164029.0 This FAQ has some good examples of how to move things around the different E times. Example 2 gives a 3.5h between feeds and a low-end A time - might give some inspiration. What sort of A times do you aim for at the mo?
HTH
Charlotte