patagonia r3 for backpacking

Yes, it's too warm as an active layer unless it's very cold, colder than what you would experience. You are really going to want some kind of lighter active layer or else you will be too hot on, too cold off.

It would be fine as a sationary layer, but down is lighter for the warmth as a staionary layer.
Still, that really fluffy polartec thermal pro fleece is going to be the warmest per ounce non lofted material you can get.
I sometimes carry heavy amounts of fleece as a stationary layer in extremely wet conditions because it allows everything under it to dry out and doesn't crap out when wet.

With all fleece their insulative ability is increased substantially (in my experience like 50% more warmth) when you wear it underneath a windproof shelll.