What kind of 'look' are you going for? Or is your motivation strictly functional? If your motivation is functional, I'd think either would work, but that at stove-top level, 30" would look more appropriate. The extra 3" on either side at the back of the stove would probably bother me much more than a 3" 'shortfall' at hood level. Jut my personal opinion, but if you're going for a 'commercial look' though, I'd rethink the idea. The combination of stainless range, splash and hood makes for a 'vertical column' effect, which might make your range look too narrow to carry off a commercial style, which I tend to think of as more 'chunky.'

Thank you to everyone for all the feedback! This has been awesome. Mcps, that looks really great with the glass and tumbled marble combo with the blue pearl. I would not normally think that those would go so well together. They do make small 2 x 2" glass tiles in the same family, although I think just the lightest blue. That light color is actually a very pale blue and not white, although it looks white on the computer screen. If I go with the stainless, I would use them sparingly as we did with accent tile in the half bath. Just need to call Lowe's and find probably 4 more sheets of the glass mosaics. They seem to be very popular. Example of accents in the bath:

Yes, shelves do interfere with venting. If the venting is the correct power and design, it will still be effective, but you will have to clean the bottom of the shelf periodically, which can be sometimes be an acrobatic endeavor. All that said, I have a large, high, stainless steel shelf and I am not sure that I could get used to not having it, despite the cleaning issue. I keep my most used bowls and mortar and pestle on it and reach for them while cooking daily. However, I suspect that you have a cleaner aesthetic than I, so you may not desire that arrangement. This post was edited by kitchendetective on Mon, Dec 29, 14 at 14:39

worthy -- Not sure, but I haven't had an issue with the stainless steel backsplash, and mine runs around the entire counter, over the sink, and on the other side. Sure beats trying to keep grout clean. The way I clean behind the cooktop is to put water in a pot, boil it so that the backsplash is covered with steam, and wipe off. The hood fan needs to be off. Of course, this method won't work for the kind of discolouration in the OP's picture, and it won't work for gas since you don't want to poison yourself by not having the hood vent on. I agree with Steve that it's a cooking area, not a work of art. It should look as if it's used and loved.