Let me counter that - if you take 10 seconds to do calcualtions in C#, then either you better run CUDA and blow C*+ away, or you are an incompetent programmer. Seriously. We do full level 2 analysis and I backtest about 1 year of futures data in 1 minute on the ES, with full L2 analysis. Real data feed does does not come close. It obviously means not doing really nasty slow SQL in trading times only before (start of day phase etc.) but hey, if you need SQL, then even CPP will not help. CPP does not magically make the database faster and seriously, I have been known to hit more than a million SQL statements to a Oracle Exadata from C# per minute.
I found the C# calculations to be no speed problem. Maybe we do not do 1 million element recalculations on every book update?