RAM always has to be as fast as the FSB on Intel boards. at 2,8 GHz you've got 400 FSB and the RAM running at 400 MHz DDR = DDR2 800.
IF your RAM really doesn't go any higher than the rated DDR2 800 then you need new RAM, another board won't help. But it schould overlock at least a little, you only need like 450, because that's where your E6300 will likely max out (I know because mine does).
On the other hand it will make more sense to get an E7200 than getting new DDR2 1000 RAM imho, that thing will overlcock to 4GHz with your current RAM^^