This is an interesting scenario. For yes in theory using an individual parameter and calculations for each of the KPIs could be faster as it only needs to run one calculation for each of the parameters changed.
Though, if you used the second method, and materialize then optimize the extract which will materialize calculated fields it could be faster.
Additionally, using the first method, could actually cause performance issues based off of the number of calculations needed to create each of the KPIs individually.
My suggestion would be to build a small test of the two different methods and test them for speed with the Tableau Desktop performance recording tool.
Another thing to consider when designing workbooks for performance is to consider a live or an extract based connection.
For Tableau Server :
Hope this helps!