I used an 8 oz. bivy (brand is escaping me, but it's a good one), on my PCT hike last year. I carried a tarp with me the whole way as well. Being wet over an extended period of time, even in warm weather, is asking for big trouble.
I used a GoLite Ponchotarp for the early stages, then a Yama Adventure Gear cuben fiber tarp...less than 7 oz., loads of protection. If you want to go light, look into cuben for sure.
The E blankets rip like a man who'd had too many beans. Also condensation is terrible, there's really no breathability. Stay away.