I have the Flipside 400 AW, it's a great pack. Actually, your current gear list would fit (tightly) in the Flipside 300, which I also have. In the Flipside 400 AW, I can fit a gripped body (5DII or 7D), two big white zooms (70-200/2.8, 100-400, 28-300) and 1-2 black lenses, or 1 big white zoom and 3-4 black lenses.
For example, packed in my Flipside 400 AW for a trip to China last year were a gripped 5DII, 16-35mm f/2.8L II, 24-105mm f/4L IS, 70-200mm f/2.8L IS II, TSE-24mm f/3.5L II, 35mm f/1.4L, 430EX II, 1.4x II Extender, 77mm 500D Close-Up Lens, a PowerShot S95, and various filters, cleaning supplies, etc. When traveling by air, I load up the Flipside, then pack that into a Pelican Storm im2500 carryon hard case, in the event that I'm forced to check the luggage.
In the image below, everything except the 17" MacBook Pro and the CF tripod/head went into the Flipside 400AW, which then went into the Storm im2500.