Maybe I just don\'t travel enough, but I am happy with my C750 battery.
Bottom line: if you are not using 802.11b then the battery is fine for daily usage. Remember any tech purchase is a drepreciating investment, but nothing dpereciates worse than money spent on rechargable batteries.
The only other significant difference between the 750 and 760 (the extra NAND flash) is easily overcome with an extremely cheap SD card
Regarding 760 vs. 860 absolutely save a few bucks by buying a 760, but I think you may have trouble finding a 760 for sale.