This overlaps a lot with these two questions: So check them out
Regarding some specifics of your question, reaction time variance will often be strongly correlated with reaction time mean. So in routine measures of individual differences where speed is the main focus, it may be sufficient to focus on mean reaction time and accuracy. E.g., mean reaction time possibly with some sort of penalty for errors (see the above answers).
If you are wanting to get very precise, then there are a range of modelling approaches that may be relevant (e.g., this question on LBA and diffusion models).
With regards to go-no-go, I believe there are fairly standardised procedures for scoring such tests.