I was checking some aftermarket gauges for my '91 NA S5 FC on eBay, these ones to be exact:

http://cgi.ebay.com/ebaymotors/ws/eB...4078900&rd=1,1

http://cgi.ebay.com/ebaymotors/MAZDA...QQcmdZViewItem

-- and I noticed that all NA S5 gauges have a 8k RPM redline... after checking my own tachometer (remember, also a NA S5), I noticed mine had a 7k RPM redline.

By chance, I came across a Turbo S5 gauge:

http://cgi.ebay.com/ebaymotors/89-91...QQcmdZViewItem

... Turbos have a 7k RPM redline?

So... NA's have a 8k redline, while Turbos have a 7k redline...

But... why does my NA have a 7k RPM redline!?

 

those are aftermarket dashes. If you haven't upgraded your engine the 7k redline is a safety measure put in by mazda. Unless I'm mistaken our engines can handle 8k redline but do it too much you risk doing some damage hence why you have a rpm buzzer that kicks in at 7.5k (it's been awhile, is that when it does it?). If you've modded your internals you may be able to push your redline up to 9k assuming you've upgraded your fuel system.