Jeddy-3, the simple answer is 'who cares'. Unless you are printing a huge mural where you need all the light you can get, always use the filters. That has the advantage that you can preserve some notional mid-tone across the grades and exposures, if you use Ilford filters on Ilford paper anyway. Of course, it is unlikely that the most important part of your print will fall on that tone, but it gives you a starting point for making changes in size and contrast.
The grade numbers do not mean that you 'must' use 'this' grade for 'that' picture. They are an accident of history. Your usual negatives will usually print around the middle of the contrast range for a usual sort of image - after that, what you do is up to what you want to see. In the Enlarging sub-forum there is a sticky-thread by Bob Carnie over his printing methods (Tips from the Darkroom), which you would find interesting I'm sure.
One exercise that used to be given to most learners was to make a grid of (small, postcard sized) prints of a neg with a full range of tones that prints easily on a mid-grade. Print each grade and vary exposure by, say, 1/2 stops across a range of a couple of stops and arrange the prints on a board so that you have your 'standard' print in the middle. Going horizontally (change in exposure) or vertically (change in contrast) you see an example of the change in exposure or contrast, by whatever units you have used, and can more easily relate what you see on a future print with what you might want to change to get it where you want.
Last edited by MartinP; 02-19-2013 at 05:08 AM. Click to view previous post history.