It turns out that reading vertically rotated text (the first example) is not much slower, as reported in this academic research (Laarnia, Simolaa, Kojoa & Ristob, 2007). They claim English readers are practiced at this to begin with, when they read from collections of upright items, like books and video tapes (for those of you who can remember). They measured the speed of reading vertical text, and reported that it is not much slower.
I remind you what @Benny Skogberg wrote about the fact that we read words as a whole (be it shapes or letter collection). I add to that another psychological phenomenon called mental rotation (Sheprad & Metzler, 1992), which shows we can rotate images in our imagination at a constant rotational velocity. By inference, we can stipulate that people can read vertically rotated words in an efficient manner, though not as that of horizontal oriented ones.
In contrast, and as Benny noted, words which contain vertically stacked letters (the second example from the question) should be harder to read. To mentally transform these words to their original form, one has to mentally re-align the letters, before the word can be recognized, and I suppose this takes a greater mental effort.
Bottom line - people would be able to efficiently read vertically oriented words, but of course not as fast as horizontal ones.