Re: 8 layer PCB???
The most important thing in 8 layered board is to 1st determine the layer stack.
in my 8 layered board case the main reason to go that much layered is due to a BGA ICs, thus we need more layers so that we are able to fan out n have enuff and strong GND and power planes
If u have address and data lines do them and also those sensitives lines 1st..mabbe u can ask the circuit designer of the sensitive lines.
Also the most important to save time is PLAN ur routing and have discussion with the cct designer, that could help alot.
If u don't plan ur address n data lines u might end up doing them again n again