I need one of those hats!!!

Have you tried a Simply Rugged yet?  I carry my G20 in a Simply Rugged Cuda with IWB straps.  Also have a Chesty Puller system, but almost never use it.  I think Rob has already made a couple of G40 rigs, so no need to send in a sample.

ETA: he also did a custom removable retention strap for me for when it's chest mounted for fishing or riding.  Don't use it much since I prefer strong side unless wearing waders, but it's nice to have.  He's a big 10mm guy, so I'm sure he would enjoy making a rig for you.

Thanks for the reference. I'll check out Simply Rugged.

I've also been looking at the Alaskan Guide Holster, as it would position the G40 center-chest, open-carry style. That's most likely how I'd carry it when hiking, camping, hunting (with a rifle), or fishing.

They're making these specifically for the Glock 40 MOSs:  http://www.diamonddcustomleather.com/Chest_Holsters.php

Normally for CCW, I  prefer an OWB rig positioned at 4-5o'clock, but for tramping around the boonies with the G40 I'd want easier access, especially if I'm carrying any sort of  gear, or large back pack, or if my hands are otherwise occupied.

Word on the street is that if one is going to carry on the chest, the Diamond D is the one to have.  I can get by with the Chesty setup as it is less frequent, but if I was looking for a dedicated chest carry option, that's the one I'd run, as well.  I may end up doing both at some point, but love the Simply Rugged pancakes for my field guns.  

I do a lot of survey these days with many miles under a pack, so there is definitely a part of me interested in the Diamond D.  Though for getting around a hip strap on a heavy load, the Wilderness Safepacker is also a pretty handy setup, if a bit slower to access.  Even with the Chesty setup, I keep going back to IWB and a high ride under my pack's hip strap.  Not ideal, but close and faster, as well as more discrete when working with different agencies, clients and crew members.  If I'm on my own, with like minded folks, or in very remote areas, or in areas that are more accustomed to backcountry carry, then I run with it out front.  Though, anytime I'm stopped, setup, or using a smaller daypack, I like the ability to disconnect the chest straps and go back to strongside.

You live in Oregon? That's Sasquatch country. None of those guns are even close to powerful enough.

Where I live we don't have to worry about 11 foot tall ManBeasts, so I would go with whatever weighs the least- your Glock 17 would be just fine.