Query performance with primary keys of different data types
i would not see this as a major issue. of course things are a little larger but if we talk about a single integer column things will most likely be lost in noise anyway. we got 24 bytes of tuple header ... then comes the data. if things are 4 bytes larger? what difference does it make in a 10 column table. 

so, no worries ... make sure that you do what is good for your app.