Since I have a free saturday since long time ago, I just did some "research" on the color temperature of my Canon 580ex-II and 430ex.
Since I don't have the professional equipment for that, I relied on shooting raw with Canon 5D (on the excellent 100mm Canon Macro) and measuring the temerature of a grey card via Lightroom (and no averaging of many shots). So, take these numbers with a grain of salt.
Variation of temperature of the 580ex-II
1/1 power: 6500K
1/4 power: 6850K
1/16 power: 6900K (Averaged from 2 shots)
1/64 power: 6950K
Variation of temperature of the 430ex
1/1 power: 6500K
1/4 power: 6800K
1/16 power: 6700K
1/64 power: 6700K
So, the 430ex and the 580ex-II are copareable -- *phew* -- so, I did the CTOs and CTBs only on the 580 ...
Temperature with CTO on 1/16 power (580ex-II)
1/4 CTO: 5600K
1/2 CTO: 4450K
3/4 CTO: 3650K
1/1 CTO: 3350K
Temperature with CTB on 1/16 power (580ex-II)
1/4 CTB: 9000K
1/2 CTB: 13500K
I havent found these numbers on the net yet, so perheps this might help some of you.
And, like you can see, to balance a hotshoe flash with a studiostrome (normally 5500K), you'll need the 1/4 CTO on the speedlight.
Addition: The golden reflector for the (small) elinchrom beatyidish brings the strobetemperature to 4400K.