lightweight fleece hoodie or really light down parka

What size are you?

Large

Edit: 6'2" 190 lbs.

I have a Bitteroot that I use for cooler temps with my quilts and a down vest for the warmer seasons. For me warmer still means nights that could get to freezing so I often augment a 40f quilt.

My down vest at 6.5oz offers a bit more loft than my Bitteroot and for me is lighter, warmer, and more compact than fleece. It is the older FF Hyperion than is similar to the current WM Flight vest.

Just another alternative you might want to consider.

I love a lightweight down hoody and a PowerStretch fleece hoody. If I had to bring only one for summer camping (i.e above freezing at all times), it would have to be the power stretch hoody. Those things are great for so many temperatures and you can sweat in them, which is something you really don't want to do with a down jacket. Down is pretty much exclusively for putting on when you are stopped.

They are two different items, one for active and the other for static use.
I would get a cheap one of each.

I have the patagonia micro d hoody, which is unfortunately discontinued, but sounds perfect for what you want. It fits like a regular cotton hoody.

http://www.backcountry.com/patagonia-ms-micro-d-hoody

Regarding Merino hoodies, Yes they exist.

I really like my I/O Bio hoodie. 6'1", 180lbs – I wear a Large and it fits snug but nice.

Re Merino base layers with hoodies- keep an eye on Steep and Cheap. I've purchased two Merino hoodies on their site. One is Icebreaker, not sure on the other one. Pricing is much better there than retail, too. Retail for Merino is ridiculous.

On sale now at http://www.ibex.com for $80 (usually $115), and they're great: 18.5 micron, which is about t-shirt weight, and with a 1/2 zipper so you can vent somewhat. I can't stand hoodies, though; have yu htought a bout getting a merino buff for about $20 (or free with the REI dividends coming soon!?!)?

Have you thought about a hooded down vest? Less weight but still with a hood.

I cant think of many off the top of my head but PHDesigns had one on sale size Large last time I was browsing there.

I get your point and use vests a lot, but I'm normally using a vest in moderate conditions with a hooded shell and a beanie or other cap. When I pack a vest, I am looking for maximum core insulation at minimum bulk and always have a beanie in the mix. The hood is extra complication.

Layering a fleecy hoodie midlayer like an R1 with a puffy vest really works, giving your arms and head that little bit extra and keeps the cold fabric off your arms if you have a shell over the whole works.

The strength of a hooded vest would be the protection provided to the neck and back of the head, which isn't needed in moderate conditions. Many have noted that too many hood layers gets to be clumsy.

As to the OP, a fleecy hoodie is perfect for cool wet conditions. If I'm going for a puffy, I want something loftier than the thin down or 60g synthetic garments. I'm always assuming that the fleece will be worn with my wind or rain shell', just like a 3-in-1 jacket. The fleecy midlayer is great for sleep too.

active or static use?

that will likely be the deciding factor in which to get

;)

Summer is when your pack is the lightest anyways, so consider if you should put the money into improving part of your kit that shaves weight across the board, rather than when you need the savings least.

You can drop a full oz off the Bitterroot easily. Inside the jacket GoLite hung an extra layer of inner face fabric so that they could add those heavy interior pockets. You can snip this layer out, ditching the fabric, mesh pockets and zippers. The change is hardly noticeable except the seams aren't quite as refined underneath which hardly matters because it's on the inside.

With that you'd have a 12oz down jacket with 5.3oz of down fill. If you go with a lighter jacket, most of that weight savings comes straight from the down fill. I.e. if you switched to a Patagonia UL Down Hoody (2.8oz down, 9.2oz total) then you've saved about 3oz but 2.5 of those ounces were down. Which means you've lost a lot of warmth for a small weight savings.

So if you really want to save weight, then you've gotta give up the hood and probably the sleeves. The Blackrock Down Vest is the best vest out there (2oz down, 4.5oz total), although it's out of stock right now.
http://www.blackrockgear.com/vest.html