I missed your original posting; I'm afraid we don't have any figures for Forté papers in house. You shouldn't need to use more than a couple of 10x8 sheets for a full calibration. Alternatively we offer a calibration service, or you could try our new calibration kit if you don't already have one.
The main thing to remember is to get the exposure correction right first, based on the highlights, before attempting contrast calibration.
Dichroic filters don't generally fade, but you might find the filter mechanism in your enlarger needs attention. I seem to recall some years ago a friend of mine having a similar problem with a Durst colour head which was traced to the filters not being moved into the light path correctly. You should certainly get up to grade 4.5 with Ilford paper from that head; if you cannot, I suggest you have the head checked before going any further with calibration.