I also have a big, "long oval" shaped head and have not found the perfect helmet yet. I currently have the Giro Synthe and it is working well-enough for me even though my noggin' is at the very limits of it's size adjustability.

I recently had the revelation that in order to block sweat from my eyes, I started wrapping a sweatband on the outside of my helmet straps so as to not screw-up the sizing on my helmet which gives me a headache. (Pictures of what I mean here) After making that adjustment, this is the first cycling season I've had in a long time where my helmet is no longer causing me head pain and I can see out of my glasses for the entire ride

I find it frustrating that the bicycle industry seems to refuse to acknowledge that heads have different shapes. While there are helmets in the motorcycle industry for "long oval" heads, no such thing exists for cycling.