LEXAPRO: WHAT IS THE HIGHEST TOLERABLE DAILY DOSE?

Hello,
High-dose Lexapro seems to be helping me a little.  I have been at 40 mg/day for a couple weeks now.  I still have some residual symptoms, however.  I have read here and elsewhere of people taking 50 mg and even 60 mg/day.  I do not know how authentic these posts are, though.
Is it safe to take 50 or 60 mg/day Lexapro?  Is there anywhere on the Internet that discusses high-dose escitalopram?  I was speaking informally to a nurse practitioner and she was saying that at 60 mg, there may be problems with heart rhythm irregularities and symptoms of serotonin syndrome, such as hyperthermia.  She said she had heard of someone almost dying at this dose level once.
If anyone has any info on high-dose Lexparo, I'd love it if you would share.  Lexapro at high doses seems to be devoid (so far) of the side effects that have always given me big problems with other ADs at high doses, most notably sedation and sweating (diaphoresis).
THANKS