Digital BW, The Print

I have an old digital only image that I'd like to print at 8 x 10 
with my quads. I remember reading on the list that even when you 
don't have the resolution to print at 240 - 360 dpi that you should 
use the resize within PS to 'create' the extra pixels -  that 
somehow this would yield a better print. 

My question: I plan on using the SI (stair interpolation) action to 
create the resolution needed to test this, but at what stage should 
I do this? On the base image before levels, curves, editing, 
sharpening etc; after levels curve, editing but before sharpening; 
or as a last step before printing?