Program built by Virtual Studio express C# with sql server express is as fast as paid version?

Its really doubtful that you will be stressing the database enough with your application below the 10GB limit that you would notice a performance problem. The multiple physical processors come into play when you start using connection intensive, multi-user concurrent operations.

When you outgrow this database, you can upgrade it to a standard version without code changes. Its the same back-end except it only uses one scheduler (hence the single cpu). If you are using that much resources, you are going to be looking into a dedicated SQL server machine (or machines, depending on load) anyway.

Hello,

It's unlikely that you will ever see any difference in performance between the express edition and one of the paid for editions.

Anyway for reference the differences are:
1) Sql express only uses 1 CPU, the paid for versions have multi-cpu support.
2) Express uses a maximum of 1GB of memory, the other editions anything up to the maximum supported by the OS.
3) Express databases are limited to 10GB as opposed to 524PB for the other editions.
4) All kind of performance features are supported by the Enterprise and Datacenter editions.

So in short yes there are performance differences, but probably none of that will ever apply to most people.

Valery.