Disappointed with Canon 600EX flash power

i Just bought a 600EX to replace my 430EX. i shoot mainly with my 24-105 F/4 and while the 430EX never let me down, using an F/4 with high ceiling meant high ISO and sometimes 1/1 power, of course with the disadvantage of low recycling.

while looking forward to  a big jump in power with the 600EX (i expected using 1/4 power as an equivalent of 1/1 on my 430EX), i have been left majorly puzzled in the couple of weddings i shot. i found myself using 1/2 and 1/1 power most of the time.

today i did an improvised testing and shot both flashes with the same settings (f/4, 1/250) and used ISO 100,400 and 1000.  on each ISO increment, i shot a series with ETTL, E+1, E+2, 1/8, 1/4, 1/2, 1/1.

Equip: canon 24-105, canon 60D and camelion 2100mAh rechargeables.

while comparing the pictures in LR and looking at histograms , at each equivalent shot (600EX and 430EX), the images look pretty similar, just a tiny minuscule advantage to the 600EX, but seriously nothing much in it.

possible explanations:

- my 600EX has a serious problem?

- my batteries not giving enough juice?

- am i doing something wrong?

- they are supposed to give the same power and i spent a shitload of money on a flash i didnt need.

Please help!