Digital BW, The Print

Sorry, this isn't strictly about printing, so feel free to reply off line ... I 
use a Nikon D70 and Photoshop 7 print on 13x19" paper. 

I wondered how much enlargement one has to do to make a program such as Genuine 
Fractals worthwhile and if the amount of enlarging I'm doing warrants 
considering anything other than Photoshop 7 Bicubic, which I currently use.

I did get Stair Interpolation Pro, but can't see a worthwhile difference from 
the standard Bicubic interpolation.

thanks,
Richard