thicker rad mean for instance - 3 rows of 13mm by 2mm Tubes compared to single row, 2 pass
FPI (fins fer inch) is where you have to decide what's the best fan for the RAD and yes ,most of the thicker RAD's are low FPI= slow~medium rpm fans
I am actually going to use the XSPC Kit since its my first WC. Since because my main motivation for this set-up is silence finding fans that our "silent" has been a chore but I am probably going to go with GentleTyphon's. But I still got more reading to do!!!