If there is doubt, add more structural support.
1" - even with the edging - may sag/warp. Deco was correct in his thinking to add further support.
Why would there be any doubt? If a shelf is designed to hold 300# and you can only put 150# on it, wouldn't that be considered adequate?
Personally, I would take the very real possibility of warping into consideration, and stiffen the living shit out of it.
I built mine with different measurements on-center because I lagged into concrete, rather than evenly spaced studs. This allowed me to space my shelf standards however I wanted. On one wall, my on-center was 19.75" so my span is even further than what is typical for dimensional lumber. With fir 1x12's as shelving it was still more than adequate and there is no sag at all, after more than a year. If I thought for a minute that the shelves were less than adequate for the weight, I would have beefed them up but since it's not necessary, it would have been extra and unnecessary work and expense.
Here's a great site if you ever have questions regarding what size lumber you need to avoid sag...
www.sagulator.com[edit]: CRAP., the site no longer exists! It was an awesome tool. I bet there are other similar sites out there.
[edit2]: Here's one that is exactly the same, including the name...
http://www.woodbin.com/calcs/sagulator.htm
