How many iu do you need? I used 5000iu at mid cycle and am using 10000iu at the end. My 5000's came as two 2500 amps. The 10000 is just one amp.
Personally I would have prefered several 2500's for that 10000 which would have allowed me to mix it every 5 days thus reducing the risk of mixing the whole 10K and having it all degrade by dy 10 or so. (yes, I kept it chilled, but still...)
other than the fact that it's sorta annoying to break the amps I cant see the advantage to the 3X1500's or the 3X5000's...