Mine ('01 S), once warmed, resides in the 180 or a hair over region. You're fine, I should think. Many here advocate removing the front bumper and flushing out the radiators, which tend to collect a lot of stuff over the years, inhibiting the cooling process. It's been on my "To Do" list for a couple of years now.
I don't recall offhand if "Peak" is an acceptable alternative to the Porsche antifreeze, but I'm thinkin' it may not be. They (alternatives) do exist. Do a search here on "antifreeze" and you'll get all kinds of info. (Here's a start:
http://www.986forum.com/forums/showthread.php?t=9112&page=1&pp=20) Mixing them can definitely be a problem. The stuff lasts a long time...I just bite the bullet and pony up the bucks for the expensive Porsche product.