The most important piece of venting a stove is that you get coverage for the burners. All of the burners :) Steam, grease and other cooking stuff does not always fly out the back side of the pot :) In particular you have a grill, so coverage is a big deal there if you actually plan on grilling ever. I wouldn't even make it a second thought, I'd bump it out at least the same as you are your stove so all burners are covered. I'd also do a bit larger hood (at least 3" on each side) to make sure I had excellent coverage.

Thank you igloochic. I did get the larger hood (42") - and I see what you mean - so I will bump it out. Neither our KD or appliance salesman seemed to think it was that important, but i'm glad i asked. Any input on how high off the counter is also appreciated... in my duplicate post in the Appliance forum, weissman suggested 30"

30" is usually the minimum recommended height. You may want 36 or higher, depending on your cfm.

Also, the reason why they make vent hoods 27 inches deep is so you don't have to bump them out, (alternatively most companies also make 24" depth).

If you are bumping out be very careful about how you mount the hood, and look at the warrantee information regarding the recommendations as to the type of material you can mount adjacent to the hood.

My cooktop is bumped out 3 inches, so I had the top cabinet made 15" deep instead of 12". I will install the hood at the front edge of the cabinet so it will still be centered over the cooktop. I am getting a 3" wide filler strip made of stainless steel to go at the back of the hood where it would normally be touching the wall. This will prevent gunk that was supposed to go up the hood from getting behind the hood instead. This strip will be attached to the back bottom edge of the hood and to the wall to seal that void up completely.

Pardon the massiveness (yes I made up that word) :oP of this silly hood but it had to cover a big range:

I believe we're 34" off the surface, but since it's just recently been all set up, I'll go ahead and do a measurement for sure and post it this evening.

We spent a lot of time on the phone with vent a hood when we had this rebuilt (we ordered a standard 1200 cfm and then took the guts out of the box and had the box rebuilt by a local stainless steel fabricator). We made sure that the power was going to be sufficient and wanted to increase capture space front to back as well as side to side. We couldn't go with a standard US measurement on a hood due to space issues and conversion from the french range size.

It's mounted to both the wall and hung from heavy chains wrapped around the beams in the ceiling. Three heavy guys did pull ups from it :) It's not coming down. It was a chore though to see it hung well. It vents out the back through a wall, but it was far too heavy even in it's metal stage to use that as the only support. Then once we applied the marine plywood, plaster, trim and granite detail..well she's a heavy girl :)

One thing I did (I hope it shows here...if not I'll take another photo) is to bump out the counter to meet the front of the stove. I did that to avoid the obvious "hip meets square edge" of the stove, and it also serves to keep you from losing an eye on the hood if you're tall enough :)

Actually here's a pic that shows the bump out better. It flows so well this way: