sqlite3 IN vs. NOT IN on same subset

sqlite3 db :memory:
db eval "CREATE TABLE pages ( type TEXT, id TEXT, content TEXT, PRIMARY KEY (type, id) ); CREATE TABLE pages_done ( type TEXT, id TEXT, PRIMARY KEY (type, id) );"
set i 0; while {$i < 10000} {incr i; set t "type$i"; set c "content $i"; db eval {insert into pages values(:t, :i, :c)}; if {$i & 1} {db eval {insert into pages_done values(:t, :i)}}}
puts -nonewline "Row counts: "; db eval {select (select count(*) from pages) pages, (select count(*) from pages_done) done} values {puts "pages: $values(pages), done: $values(done)"}
puts "IN:         [timerate {db eval {SELECT type, id, content FROM pages WHERE (type, id)     IN (SELECT type, id FROM pages_done) LIMIT 4999,1}}]"
puts "NOT IN:     [timerate {db eval {SELECT type, id, content FROM pages WHERE (type, id) NOT IN (SELECT type, id FROM pages_done) LIMIT 4999,1}}]"
puts "EXISTS:     [timerate {db eval {SELECT type, id, content FROM pages p WHERE     EXISTS (SELECT 1 FROM pages_done pd WHERE (pd.type, pd.id) = (p.type, p.id)) LIMIT 4999,1}}]"
puts "NOT EXISTS: [timerate {db eval {SELECT type, id, content FROM pages p WHERE NOT EXISTS (SELECT 1 FROM pages_done pd WHERE (pd.type, pd.id) = (p.type, p.id)) LIMIT 4999,1}}]"

# results:

# Row counts: pages: 10000, done: 5000
# IN:         1599.02 µs/# 626 # 625.38 #/sec 1000.988 net-ms
# NOT IN:     935942.5 µs/# 2 # 1.068 #/sec 1871.885 net-ms
# EXISTS:     2761.25 µs/# 363 # 362.15 #/sec 1002.335 net-ms
# NOT EXISTS: 2754.40 µs/# 364 # 363.06 #/sec 1002.602 net-ms