6.51W is good from those panels
i have one like your panels , and one larger one (rated at 5W) and the most i've seen from them hooked together is just around 4watts and change , so you have done well.
i've got one of those radio shack multimeters too ,the oldest one i've bought , and by far the best one i own , as far as least amount of problems that i have had from it..plus it runs on two AA cells , not a 9V battery , which is nice..
just last night i disassembled one of the other multimeters because the top of one digit was faulty, luckily it got back together and is working now , but its still a piece of crap compared to the radio shack one.