Build a spreadsheet that compares the regular and condensed proportions of fonts you like and let that guide you.

Why don't you just create something that you like?

Once you finish it you can decide to call it condensed, compressed, narrow, or something else.

But it really should be something you like or think will be useful.

I remember that article. This TypoWiki is dead but the procedure is simple: having to extremes, one regular and one bold, make an interpolation ONLY in the horizontal axis. The resulting font is a good starting point for a condensed version. Cheers.

If you have a regular and a bold then you can try using the RMX Add MM width Axis macro, which is part of the Font Remix Tools: http://remix-tools.com. There is also a video on the website.

If you are interested in the question which weights (also interesting: which glyphs) are typicaly condensed how much compared to the others then you might find the PDF on the "About" page interesting, which presents some research I have done on that subject.