You would change the CPU to RAM ratio only if you have RAM that doesn't overclock well. Lets say for instance that your CPU can take 300 MHz, but the RAM can only take something like 250 MHz. When you raise the FSB (HTT with an AMD) it will automatically raise it for the RAM as well, so you must set up a ratio if the RAM is maxing out and your CPU isn't. For instance, if you set up a 5:1 ratio, if you increase the FSB from 250 MHz to 255 MHz, the RAM is only going to get 1 MHz more instead of 5 more.
The only way to find out the max FSB your motherboard can support is if your CPU can be overclocked (and is stable) further than the motherboard can go. Other than that, there is no way to find out the max FSB the motherboard can do.
CPU: Intel i7 2600k @ 4.4 GHz
Cooler: Cooler Master V8
Mobo: ASRock Z68 Extreme3 Gen3
RAM: Corsair Vengeance 16 GB DDR3 1600 MHz
GPU: EVGA 560 Ti
HDD: Cruicial M4 SSD 128 GB
HDD 2: WD VelociRaptor 300 GB
PSU: Corsair TX650w
Case: Corsair 600T Graphite Series