Hi!
Not that I'm an archeology fan digging such old topic

, but for the sake of order I decided to add my experiences here. So, recently I bought NGK iridiums at a good price on ebay, mounted them, and....
First of all, like many of us, i know my bike very well - we've been riding for a while, so I could compera it really well. And what are my remarks? well, I wonder how i could have gone without them for so long!!
aha! Spring has sprung very early here, in fact there was hardly any winter, so I'm riding quite often now. So, it's early morning (say, today), 7am, -3 deg Celsius (that's, say 25F), bike stood for a couple of days in unheated shed. And I'm living in the mountains. Normally it would be a bit of ordeal to get it firing, but now it's choke full, twist the gas few times (for acc.pump to spray some fuel) and brrmmm, engine is working. And now it's the best part. Usually I would need to go on choke for first kilometre or mile. Now the choke can be off FULLY after half this distance, AND (I like this part the best), since I live in the mountains, first 2-2,5 miles are downhill, so in summer, I just go "economy" without the engine, but now I want to warm it somehow. Ordinarily, that's a tough thing, to ride 30-40mph in cold air, on idle, and keep engine running. I know, I had this problem many times before. Now, engine purrs at low revs (around 800), but super-steadily. And when warmed up, idle suuuper smooth.
Now riding - less dramatic changes, but better response, and overall "smoother sailing". And there is the mileage perk as well.
So - don't think about it - go and but them. In your (USA) paradise of cheap and plenty, they are for 6-7$ a pop, so there's no argument about the price anymore.
Enjoy!