If the data source is a column in a collection, you can use Linq to run aggregate SQL queries against the DataTable, such as max(). If you're only working with two numbers though, it should be fairly simple with a decision stage to see which is larger.
[Decision][x]>[y]?
Yes -
[Calculation]In: [x]; Out: [Value]
No -
[Calculation]In: [y]; Out: [Value]