Hello,
Thanks for sharing your experiances about LiPoRider Pro and solar panel with the community. The solutions that you have tried are almost ideal when tradeoff between cost and efficiency are considered. LDO looks to me as best solution for your situation. I think the overall power produced is important. We should not bother about the wastage in noon for a low cost solution.
Also post your requirements for DC-DC convertor (input voltage range, ouput voltage = 6V ?)
Let us see if any community member has other solutions.
Thanks and Warm Regards