Do any of you know of a lighter battery for a trolling motor that will give at least 6 hours or so of use? I'm looking for a lighter one for my one man pontoon craft.

It ain't to be had unless you're wanting to spend some mega bucks.  These new technology power cells like they are using the electric vehicles are about the only thing that's going to do what you're talking about.  Even if you could find a 12 volt one with the AH capacity your talking about, you would have more in a battery than boat and motor.  There are lighter batteries but they don't have the AH capacity a good lead acid deep cycle.

I know the weight difference isn't too drastic but how about an optima?

I WOULD RECOMMEND AN OPTIMA BLUE TOP BATTERY...ITS A LITTLE PRICEY BUT WILL LAST AT LEAST TWICE AS LONG AS A CONVENTIONAL BATTERY(THE PRICE EQUALS OUT IN THE LONG RUN) ..I HAVE A RED TOP IN MY TRUCK & IT IS LIGHTER THAN A REGULAR BATTERY & IVE NEVER HAD A PROBLEM WIH IT.

GOOD LUCK

AGM batteries will not give the run time a similar lead acid battery.  Yes the Optima is a few pounds lighter, but they also have less run time.   The main benifit to the AGM, you don't have to worry about keeping them charged like you do the lead acid batteries and you don't have to worry about the acid making a mess in the boat.  

This is strickly my own personnal opinion but for my use, someone would have to give me Optima's for me to use them because I would never pay twice (or three times) the cost of  a good deep cycle lead acid battery for battery's that will give me consideralble less run time.    Now if I took numbers of trips where it may be two or three days before I could get my batteries fully charged again, the Optima would be a great battery to have because that would play havoc on a flooded cell lead acid battery.