Streamline a large engineering software package built in C# .NET

We are engineers who have programmed a software package to perform intensive engineering calculations. While we are confident in our calculations and results, we believe there is room for significant speed improvements. There will be a fixed-cost, two-week evaluation period at the onset of the project, during which the candidate is expected to become familiar with our calculation engine and identify surmountable inefficiencies. At the end of the evaluation period, based on the candidate's findings, they will be offered an hourly rate to repair these inefficiencies, as well as to continue identifying additional areas for improvement. We are happy to continue this process for up to 3 months as long as continual enhancements are being made. We have a number of existing unit tests and projects that can be used as benchmarks, both to confirm speed improvements, as well as verify that no actual calculated results have changed. The candidate is expected to have substantial previous software engineering experience, with a strong background in .NET and C-based languages. Expertise in intensive engineering/mathematical computations is a plus.