I've worked extensively with both SQL Server and Postgres and money being no object, there are valid reasons to investigate both. SQL Server's query planner is better, Postgres has only just got limited parallelism for some sequential scans, and still treats CTEs as second class citizens. Postgres in version 10 is going to get proper partitioning, which SQL Server has had for years. There are vast numbers of feature differences, down to individual GIS functions one platform has over the other.