Quick question, but a little more complex than a simple yea or neh answer. Living up in Lubbock, (elevation ~3200ft) the highest octane gas they sell is 91. On the otherhand in DFW with an avg elevation of ~500ft, I can find 93 octane fuel almost anywhere. I did some internet research and apparently the reason being for this is that due to the lower oxygen levels as elevation rises, the engines have to work a little harder to combust the fuel they are running. So my question to y'all is...

A) If the goal for higher octane gas is to reduce possibility of engine knock, will 91 achieve the same result as 93 at this elevation?
B) Is it just coincidence that they don't sell 93 here, and I am really going to fuck the engine up pushing it with the 93 tune?

Thanks again guys, I freakin love the 93 tune, but I'd rather be safe than sorry!

Chris