Pottery Barn has clear globes for around $150 but the size is larger than you are looking for. http://www.potterybarn.com/products/calhoun-glass-pendant/?pkey=cpendants West Elm also has clear globes (modern look) on sale for $99. Also might be to big. http://www.westelm.com/products/a563/?pkey=cpendant-lamps-chandeliers

The original fixture dimension seen in the front porch picture is ~30”H x ~12”W. The lighting store suggested larger scale. The new Mills Large Hanging Lantern arrived today. Its dimension is 34”H x 18.25”W. Has this new fixture been overscaled for this space? There was a medium option, but the dimension was shorter (~26”H x ~14”W) than what is hanging now. Should I hang the fixture centered to the second floor window above the door or the wall space between the door and window?

What Millworkman said and opening that ceiling would be like opening a can of warms and most likely you will end up reframing everything. Just did a complete renovation of 2 houses built around the same time your house was built and everything has to be reframed under there, because as soon as we took down T&G planking, everything above fell apart, they had a few 2x4's over-spanned holding up that planking.

I have the same pendants as @mihelene. I have NO issues with glare although plenty of folks on this site warned about that and said it would be a problem ----- it has not been. I will second, though, that they do have to be cleaned regularly and that is another task to keep up on; although I often wonder if I had something not clear, surely it would be getting just as dirty and need cleaning.....? Maybe I should just feel grateful that my lights make me keep a cleaner house. ;) Also, it seems to me that the height of your ceiling isn't such an issue as the height the pendants are recommended to be hung is 30-36" above your counter top regardless of what height your ceiling is. I have 9' ceilings and my globes are about 15.5" long. I don't think an 8' ceiling would be a problem. (My sister in law has 8' ceilings and she just installed fixtures similar to your posted picture. They seem bigger than mine (perhaps just in width) and they look good.)