In short: everything is easier to understand if you operate on base clocks( Fsb 800 really runs at 200MHz, ddr800 ram runs at 400Mhz, if you want to know why than google Quad Pumped FSB nd DDR respectively)
As for e5200, its higly unlikely that it will go beyond fsb 333mhz, mine maxes out at 330mhz. Remember its a budget chip.
I've tried over and over to overclock my e5200 on two Asus motherboards capable of fsb 2000. I could not get the e5200 to 1333, would not even post. It's completely stable at 1066 24/7 at the same volatge as on stock speed 1.2 vcore!
On the stock Intel HSF both cores "only" goes to 61 C after 30 minutes of Crysis, Far Cry 2.
Doubling the FSB would double the clock speed -> 5ghz on an E5200 is unheard of on any air or water cooling, even an 8 series would struggle to see past 4.3ghz even messing with the multiplier to get there
Better option - set the ram for 1:1 if you can and clock it up that way to get the max out of it (so in the end its the cpu thats maxed, not the ram or motherboard), and as for higher ram speeds, anything beyond 1:1 ratio (eg 800 fsb with 1066 ram) wont see any benifits or minimal at best.
You will definitely see a difference running that e5200 from stock 2.5 GHz to 3.3 GHz on a 1066 bus. Just leave your RAM at stock settings for a 2:3 ratio as you'll have to underclock it if you want 1:1 which will slow down your system in this case.
I tried doing exactly what you said. It seemed to me to get a good 1:1 ratio with the ram (800 Mhz), I wanted to set the bus to 400 Mhz (1600 Mhz FSB). If I did that, I knew my E5200 would not run at 5 Ghz, so I planned on reducing the multiplier to a more reasonable 8 (3.2 Ghz). This would make the FSB mesh well with the ram and allow my ram to use its full capabilities, all the while giving me a nice overclock. However, I have not been able to make this work, and right now I have my E5200 at 266 x 12.5 for a 3.33 Ghz system. My ram is still running at 800, but has a divider and is not running at 1:1 ratio.