Aaron,
The shorter tip isn't a colder plug it just has the same effect as one. Like Ryan (Tazer) said get the Iriduims and you will like them. They burn hot and clean and are fine for daily driving or high boost and nitrous.
I perfer the standard length tips (NGK-TR51IX 7316), and believe they are actually a couple rages colder than the standard double platnuims. I had a set for about 6000 miles and pulled them out trying to find a problem with warm restarts. The plugs were perfect and have now made there way into Chris Wise's engine, so I just ordered another set for use with my nitrous kit.
David