Depends on which flavour you want to dominate: honey or berry. If you want honey to dominate, use less fruit. I try to go for a balance, but it's often tough to get enough fruit to avoid the "weak" or "watered down" fruit flavour without masking the honey flavour.
You might start with 1 PINT of fruit per gallon, you'll get more flavour if you put those berries through a freeze/thaw/freeze/thaw cycle; it helps to break down the cell walls & extract more juice. If you find that it needs more than that, you can always add more; but once added, it's tough to remove it.
You could also start with 1 POUND of fruit per gallon for more fruit flavour. Here's a recipe you might find useful: http://www.homebrewtalk.com/f80/blueberry-mead-34038/
It starts out pretty much the same as yours & uses 1lb/gal fruit. Thought you could read thru that thread & get a feel for his end product & adjust your recipe as you see fit.
One thing to remember, fruit not only takes up volume, whole berries will swell & take up even MORE volume. Also, use some pectic enzyme, it'll help in the breakdown of cell walls & help to extract more juice & flavour as well as help to clear by breaking down the pectins. Mix any dry powders with a little boiled & cooled water before adding to the must. Adding dry powders will provide nucleation points & allow the dissolved CO2 to suddenly come out of solution, like a mead volcano.