I have 52/42 on one of my bikes. As others have said, the difference going to 53 would make is not worth the trouble. I do notice the difference between 42 and the 39 I have other bikes but its not huge. If you haven't already maxed out your rear freewheel/casette -- I am guessing freewheel since a 52/42 set up is kind of old school so am thinking we are talking about an older road bike -- you could go as big as 27 or 28 tooth large cog and, paired with a 39, generate a more noticeable change on the low end.