I haven't noticed any speed diffirence in 1.8 vs 1.77.
My List is around 150K, and I normally get around 50-80K / hour. This means it takes around 2-3 hours for a mailing to be pawned off to the mailing machine, normally small emails, text only, under 10K.
Done with 2 machines, one hosts the DB, the other is a dedicated Mail Machine running sendmail.
Of course once the mail is pawned off to the mailer, it takes it more time to complete its job.