Sonoma sure didn't seem all that populated when I visited. With the exception of Atlantic and maybe a couple of others, I don't think you will have too much trouble placing a max secure house on any shard even in Trammel...location may not be ideal but there is space.
(As a side note, I visited nearly all of the Asian shards on a deco recon mission recently, and was kind of stunned at the huge open tracts of land with sparsely scattered houses, in what is usual the high-density trailer park of UO sections on other shards.)
-Skylark
