It turns out that reading text vertically rotated (the first example) is not much slower, as reported in this academic research (Laarnia, Simolaa, Kojoa and Ristob, 2007). They claim that English readers practice this to begin with, when they read collections of vertical articles, such as books and videotapes (for those of you who can remember). They measured the reading speed of the vertical text and reported that it is not much slower.
I remind you what @Benny Skogberg wrote about the fact that we read words together (either forms or collection of letters). I add to that another psychological phenomenon called mental rotation (Sheprad and Metzler, 1992), which shows that we can rotate images in our imagination at a constant rotation speed. By inference, we can stipulate that people can read vertically rotated words in an efficient way, although not like horizontally oriented words.
In contrast, and as Benny pointed out, words that contain vertically stacked The letters (the second example of the question) should be harder to read. To mentally transform these words to their original form, one has to re-align the letters mentally, before the word can be recognized, and I suppose This requires a greater mental effort.
In short: people could read vertically oriented words efficiently, but of course not as fast as horizontal ones.