I can think of a couple ways to count the number of rows in a table with Laravel (version 3).
DB::query('SELECT COUNT(*) FROM threads;');
ceil(DB::table('threads')->count() / $threads_per_page);
MAX(ID) is not the same as counting rows, so that rules out two of five alternatives.
And then it is your task to actually do a performance comparison between the remaining three methods to get the count. I'd think that actually executing an SQL statement directly might remove plenty of unnecessary ORM-layer overhead and be actually faster, but this would be premature optimization unless proven by facts.