Koz,
I just read your post on your 3.4 V6. Quite interesting the differences and the similiarities. My plugs were also split evenly the NGK's were all on the drivers side and had noticeable erosion of the electrode in my engine. The Densos looked very good with the exception of some blow through on one insulator which I have seen on many different makes of plugs at different times. Between these 2 particular plugs I'd go with the Densos. If I can get the picture resized to fit as an attachment you could see the differences. Not all plugs are created, equal even under the same brand name, and will burn/erode at different rates because of many different factors. In this case I think the electrode in the NGK's was the factor. We have Denso coil packs in our Toyota's.