I have a similar situation with an ASUS P5Q Pro & e4500. soon as i installed the e4500, straight out the gates, i upped the FSB from 200 to 266 to yield a 2.926 speed, i have not tried anything else yet, but i will when i get home and see what i can mess with. FYI, i have 4G DDR2 - 800 RAM as well, so we have similar setups...
As of late, with my Xiggt HS/F my temps are 20c idle and 38c load so i will have plenty of room to work with.
Stock vcore on my setup is 1.38v or (1.376) and i think 1.52 is safest high point, so i wouldnt go beyond that...
I'll keep you posted...
As for the 1:1 Ratio, it's not necessary. It's basically the sweet spot, but it'll have minimal effect to have it at say 3:5 or 4:5... just as long as your RAM is not boosted too high for frequency...