Optimize for taste, not for fast growth, please. I don't want to pay for lettuce with taste of straw.
Iceburg seems to be intentionally useless. Romaine starts to have a little flavor. Leaf lettuces have a wide range of flavors.
The result is a very flavorful salad- intensely bitter with much less crunch.
http://sweets.seriouseats.com/2008/09/chocolate-cocoa-butter...
Optimizing for anecdotal data is one of the things I'm working on, it's amazing the depth you need in selecting specific traits to breed into plants.
No one tastes locally grown produce and thinks, "this is OK, but I really prefer the flavor of the produce that's genetically engineered to not bruise as easily in shipping."