Hit a rut overclocking my intel core 2 duo e8500

Hey guys. I know my cpu is old but I want to get everything I can out of it before buying a new computer. My cpu has been bottlenecking my computer for Battlefield 3 so I decided to try overclocking the cpu (my video card is the radeon HD 4850 x2, another old part but it only going through about 60% usage while my cpu is going through 95-100% usage when gaming). So far I have overclocked to 3.8 GHz (FSB @ 1600 MHz, x9.5, Memory @ 800 MHz). I set my BIOS core voltage to 1.4 V (which translated to 1.36 V in CPU-Z) and my memory voltage to 2.0 V. I am using the nForce 780i SLI motherboard. I also have a pretty good Thermaltake cpu heatsink. I built this computer about 3 years ago and haven't really done anything with it since then.

While testing with Orthos, it seems my cpu temp goes to about 60-63 degrees celsius (40-43 degrees while idle). If I try increasing the FSB anymore, I can't get the computer to boot no matter how much I increase the voltage. Does anyone know what the cause of this is? Is it a heat problem? I can't even boot my computer to check the temps. Should I try replacing the thermal compound? Is my motherboard just bad for overclocking?

I've seen people get to 4.1-4.2 GHz with this cpu and my goal is to get to 4.0 GHz.

Also, a side question is which cpu voltage reading should I trust? My bios says it is 1.40 V while CPU-Z says 1.36 V? Is it safe to try voltage > 1.45 V in bios if it translates to a lower voltage in CPU-Z?

Thanks for reading and any comments!

Also, when I overclock my FSB higher, should I continue to keep the memory at half the frequency (by increasing it past 800 MHz)?

Can you explain what this RAM ratio/clock is? I am new to overclocking and the only things I know about are the FSB frequency, the memory frequency, the core voltage, and the memory voltage. I haven't changed anything else. I'd also like to note that I try to keep the memory frequency at about half of the FSB frequency. If I make it lower, my pc will only start in safe mode. If I make it higher, I see no difference (the computer still freezes at random times after booting).

Basically when I increase my CPU past 3.8 GHz, it will boot fine but freeze at random times after booting. Even if I increase the voltage significantly, nothing changes.