My aging CP-E2 pack fell out of my shirt pocket, today, while shooting a wedding with my 550EX. A couple tabs broke and the only way to keep the battery door closed is with an elastic. I have had this thing fall a few times, no damage, but I was tempting fate more than just once as the thing made a thud as it hit the ground; it's time to move on. I like the idea of a 8-cell magazine that slides in and out of a pack instead of the somewhat cumbersome way the CP-E2 loads. After viewing the specs on both the CP-E3 and CP-E4, it seems the latter is a bit more moisture resistant and designed more for the 580EX. Is the recycling time any different between either pack? Is it worth the extra $10 for the newer pack? B&H sells the CP-E3 for $139.95 and the CP-E4 for $149.95, and I should get an extra magazine for another $35 or so. Any thoughts?