Mike, I've got a Giro Targa and a Giro p1sspot. There is a difference in weight, but it's so small that you can't tell the difference when riding.
What does matter is that the p1sspot has larger foamier pads, and is more comfortable by miles - but hotter in summer. And the peak on the Targa is great for keeping the sun out of my eyes.
I've recently bought the Xen and it is a little heavier than my original helmet, a havoc. I got it because it was the most comfortable helmet that I tried on. The weight isn't really an issue as I don't notice it once I am riding. One thing about it is that it is a bit hotter than other helemts so I do tend to sweat a bit more.