First, on a single processor with HT a favorable compute bound process might see 20% improvement in performance (10% to 30%).
Second, SQL Server might be serializing your requests.
Corruption should not occure. hat you are interpreting as corruption may be perfectly reasonable for what you are requestion of your program.Keep in mind that you may need to place your console output routine in a critical section to avoid inteleaving of display within a record. Permit records to interleave but not data within a record.