Cold or Hot plugs?

Ok so im not a total noob but I need some light shed on this subject. I keep getting conflicting answers depending on who i ask.

I have a 90 ST with a A4-FE. Rebuilt at 250k and now has 310k. I live in Las Vegas where is gets VERY hot. I have played with the timing on the engine and got it dialed in to where there is no knock even under a load. Here is my question:

For better fuel economy/power, should I run Hot or Cold plugs? And If I run hot or cold plugs where should I adjust the timing? IE: Cold plugs = retard / Hot = Advance?

Right now I am running hotter plugs with the Timming advanced (i think. I have to check). and it seems to get about 35mpg and has crap power at low end.

Any help on this basic Spark plug question would be great.

If I remember correctly from my hot rod days, cold plugs burn off deposits more slowly than hot plugs, but can stand more advanced ignition timing. So cold=advanced, hot retarded. Use hotter plugs if you have trouble with plug fouling.

(Subject to the reliability of my memory)

Update:
Here's a reference that seems to agree with my memory (and a lot of additional details):
http://www.ngksparkplugs.com/techinfo/spark_plugs/techtips.asp?nav=31000&country=US

WOW!!! Lots of GOOD info there on NGK's Site!! THANK YOU for that link. So it looks like I will be making sure I'm running a colder plug and retarding the timing a bit. Came to this conclusion based on the fact that I push the little 4A-FE way too hard all day long driving around and the fact that i live in Las Vegas. So, colder plug to dissipate heat better and retarded timing to do the same. Anyone want to correct me on this please feel free.

Thank again for the link.