I used ADEX subway tiles for my kitchen. The reason I used them is because I wanted something pure and milky white. ADEX tiles are an opaque glaze over terracotta tile and just have a slightly different look to them. You'd think that would be less white than a tile with a white base but it's actually MORE white. I believe these were about $5/sf. IMO (and this is just my opinion) unless you are looking for a specific color or specific trim pieces, there is very little reason to go above generic daltile/AO subways to any of the other subways (and unless you are going for all white, people have successfully mixed and matched less expensive field tile with colored trim pieces from other lines and the results have been beautiful. But as far as the shape and look of the tile - there's a pretty small difference between generic subways of different lines (not counting specialty subways like period reproductions or beveled or handmade looking etc). Like I said, the reason I went for the ADEX was the milky white color that didn't look off next to my appliances and bright white trim. As far as how they look installed though, there's not a huge difference between those and the cheapies. Here is a picture of my far better crafted backsplash (because I did it myself, SOB) This is before the trim was painted white though.

Daltile has every trim known to man. What you want is available. You just may be searching for it using the wrong term. Try chair rail or shelf rail.

That's a nice shower. I believe we used a 2x4 accent in our 4x8 shower because the tile walls wrapped around and we wanted the smaller tile for the vanity backslash. I know you said it's not enough of a size difference for you but this is what it looks like. I wanted to use a pencil tile between the 2 different sizes but DH didn't want to because of pooling water, difficulty using the squeegee to wipe down the walls, etc. I really like the way it turned out and the clean lines!

Are you sure you can't use 3/8" thick? These come in a multitude of colors: http://www.completetile.com/products/ceramic/vermeere_ceramics/ceramic_tile   and there are liners, bullnose and other trim pieces available.