NOT the pepper tree - despite the name, they are from South America (Brazil or Peru), and are invasive in FL - I don't know about CA. They are also messy, and some people react - badly - to handling the leaves and berries, or to a scratch from a twig.

Both the others will get to 60-90', and to about 20-25' wide, so decide if you want a "green wall" to that height. It is my understanding that Leylands are somewhat more subject to disease/problems than the Steeplechase.

You might look at some of the Chamaecyparis selections, both the C. obtusa, Hinoki False Cypress, and C. thyoides, White Cedar, for a selected, tall form. Others of the Thuja family might also work, both in the T. occidentalis and the T. plicata selections. Most of these would be a little shorter than the Leylands. If you wanted a less uniform look, you could mix and match among them. Another benefit of that approach would be that if, heaven forbid, one died and had to be replaced, the replacement wouldn't be so obvious. Which brings to mind - is the developer guaranteeing these trees for a year or more, or will that be the responsibility of the nursery? Most wholesale nurseries sell trees - planting, and guarantees, being the responsibility of the landscaper or developer who planted the trees.

Of course, all this advice means nothing if you can't find the tree you are thinking of, in a large enough specimen to do you any good any time soon. I think I would do a little web surfing, and then call around to the whole-sale nurseries and see what they have in a 15-20 gallon size. Being able to tell the developer where he can get the trees might gain some good will on his part.

As well, ask if he or you will be doing the watering? It will take a fair bit of water to keep large trees happy and looking good, so find out up front who will be responsible for it, and for DOING it! And get him to pay for and spread mulch around the trees, as part of the planting process.