A simple question about text fields

Are there performance issues with the choice of 'text' vs. varchar and some character limit?  For instance, if I have a table with ten million records and text fields that may range in length from 15 to 150, can I expect a measurable improvement in response time for using varchar(150) or will text    do just or nearly as well. 

If the latter is the case, using text across the board is a simpler choice