A few practical points
Just wanted to make a few points based on my knowledge of batteries. Most of this can be found the Battery University website.
Battery capacities will vary from the marked value for many reasons, including their age and their storage history. This doesn't excuse the fakes but it does explain why the OEM battery doesn't match the printed capacity.
When testing your new battery you should run it through a few full charge cycles to reach full capacity before you start running the tests.
Deep discharging (anything below 15%) is not good for your battery. Don't over-test.
Heat isn't good for the life of your battery. Keep fast discharging to a minimum, too.
Going by anecdotal evidence from users the HTC OEM batteries seem to vary a lot. This is probably due to the varying age and storage histories with the suppliers. My phone was one of the cheap ones through Asda in the UK. I have no idea how old it is.
I have bought two Anker 1900mAh batteries and an AIO 3500mAh extended with backplate, all via Amazon. The Ankers are noticeably better than the OEM; the AIO is easily twice as good as the OEM, but if the Ankers are 1900mA I'd guess it was around the 3000mAh mark. Not as good as the Seidio, but quarter of the price.