Yes, yes - JUST when you feel like you have it, they go and change. HOW DARE THEY.

I know that exact feeling...
Definitely not the expert, but I'd think that growth spurts would be counted by adjusted age.. and if I remember correctly, there's a pretty big one at 6 mos..
As your LO goes through these developmental milestones - starting solids, rolling, etc - , things definitely get a little crazy... But I'd think that at 6 mo, you definitely want to push towards a 4 hr EASY.. I think L made it to 4 hrs by about 5.5 mo...
The biggest reasons for going to a 4 hr EASY are that a) they are able to stay awake longer - i.e., increase A time - and so a 3 hr cycle naturally becomes too short and b) they can go longer between feeds. For us, that was the sign to slowly push towards a 4 hr EASY... L just wasn't hungry anymore at the 3 hr mark.. so instead, she'd only snack-bf, and then end up hungry and night, increasing NWs.. finally getting to the 4 hr EASY made life much better.
Here's a link to a helpful sticky:
http://babywhispererforums.com/index.php?topic=63161.0HTH