I flashed Siyah's 2.2 beta 6 and used 2nd core by Tegrak to turn off the other CPU just to test it out. Never encounter any reduce in performance at all. But it did improve my battery life by roughly 25-30%.

btw, you are able to change the charging current using "Voltage Control" with this kernel. However, i've not noticed any faster charging speed eventhough i've changed it to 950mA

try using Siyah 2.2 beta 6

I'm using an ipad charger, which is 2.1A max

I'm curious on what operations or which apps do actually need the 2nd core to work well. After turning off the 2nd core for about a day, testing games, apps and web browsing, I find no difference at all from turning dynamic hot plug on.

by default it is running Dynamic Hotplug, which means only 1 core is on, then 2nd core comes on when its needed. Using custom kernels like Siyah's latest allow you to change it to run only on 1 core permanently. (with the help of an app called "2nd core")

is checkROM using touchwiz 4.5?

what CPU govenors are you guys using on Siyah? found lulactive to be OK on performance yet not so good on battery.

interesting... on which version of siyah?

try "Voltage Control". its a better app compared to SetCPU, if you're using Siyah.