Is there any definitive evidence that setting to CDMA only mode actually has any impact on battery life for a device used in the US?*
If a phone is happily camped on your Verizon home network, it doesn't go off looking for a GSM/UMTS network since there is no reason to find a network. *They D2G locked out US GSM/UMTS carriers, so again the phone can't go off looking for anything other than Verizon if you're in the US (assuming you are in civilization with coverage and haven't swapped SIM cards).*
Based on this, I don't get the claims of improved battery life if world mode disabled.