Okay, finally let it run to completion, and it indeed took ~30min over here.
(That's with the NLTK stuff disabled).
Code:
Count Page/Word Statistics
do_count_statistics - book_path=/tmp/calibre_4.5.0_tmp_Cq86l_/1PH1R6_count_pages/6379.epub, pages_algorithm=0, page_count_mode=Estimate, statistics_to_run=[u'WordCount', u'PageCount'], custom_chars_per_page=1500, icu_wordcount=True
do_count_statistics - job started for file book_path=/tmp/calibre_4.5.0_tmp_Cq86l_/1PH1R6_count_pages/6379.epub
-------------------------------
Logfile for book ID 6379 (Complete Works)
Found 1155998 words
Method of counting _page_count_mode=Estimate _download_sources=[]
results= {u'WordCount': 1155998, u'PageCount': 4259}
Found 4259 pages
6379
do_statistics_for_book: /tmp/calibre_4.5.0_tmp_Cq86l_/1PH1R6_count_pages/6379.epub 0 Estimate [] [u'WordCount', u'PageCount'] 1500 True
Estimated accurate page count
Lines: 132049 Divs: 773 Paras: 42789
Accurate count: 4259 Fast count: 3122
Page count: 4259
Word count using icu_wordcount - trying to count_words
Word count - used count_words: 1155998
Word count: 1155998
Replicated @snarkophilus's experiment with the editor (i.e., a bigger DorianGray.htm), and that still "only" takes at most 6 or 8s to HL.