My application reads an Excel file using VSTO and adds the read data to a StringDictionary. It adds only data that are numbers with a few digits (1000 1000,2 10
Unless you are 100% certain of your inputs, which is rarely the case, you should use Double.TryParse.
Convert.ToDouble will throw an exception on non-numbers
Double.Parse will throw an exception on non-numbers or null
Double.TryParse will return false or 0 on any of the above without generating an exception.
The speed of the parse becomes secondary when you throw an exception because there is not much slower than an exception.