varchar(n) and text

According to http://www.postgresql.org/docs/8.0/interactive/datatype-character.html

I always use TEXT, for column which store text so that I need not to worry on text length.

However, in certain situation, I know that my text length will always < 10 characters

I was wondering, if I using TEXT, will there have any overhead on

(1) storage space?
(2) query performance?
(3) write performance?

Shall I just use varchar(10) ?

Thanks!

Thanks and Regards
Yan Cheng CHEOK