200x12.5 is what I use too actually, with 1.85vcore.
Always go in 5mhz increments, but you dont adjust the CPU/DRAM ratio, you want to keep it 1:1 as far as you can so you'd just leave the ratio at 3/3, 4/4, 5/5, 6/6 whichever one you have it it......if you have crappy RAM it's not worth raising the FSB and keeping the RAM at 200....it's pointless and will give you no performance benefits whatsoever, will make the chipset hotter and could cause more instabilities to try and work out.
I can't tell you what timings to stay with because all RAM is different, this is the point of overclocking is tweaking your settings, finding out what the RAM will run at in terms of voltage and timings.