Unleaded Plus vs. Unleaded Premium

[Rob-00BoxsterS]

Sorry to go OT but I found this interesting:

I also own an old Nissan 300ZX turbo and frequent a few Z31 sites. A thread was started almost identical to this one on one of those sites and I pretty much did a cut-n-paste from my above written posts.

Instead of respectfully pointing out the flaws in my data collection or seeing how the data could be beneficial to them (like what was done on this site) they turned it into a pissing match on what octane ratings mean. I was also called stupid for trying to say I know the car better "then the people who made the car from ground up and tested it's flaws.” (<= direct quote from that thread.) The data was ignored while the members there competed in a game of "Who has the bigger e-penis."

This forum and the Land Rover forums are the only two I have been on that show respect to their fellow members and talks to them like they would if they were face to face. It's very refreshing.

**Note** This post is not meant to bash on other sites, just to compliment this one. Unfortunately, this site provides no information on my other vehicles no matter how hard I search so I do need to continue to frequent them.

[raddoc]

As the price of all gas rises the differential between grades drops as a percentage of the overall cost. What was a 5% difference at $.10 /gallon premium vs. midgrade on $2.00/gallon gas is now only a 2.5% difference. It makes less sense than ever to use lower grade gas , as long as there is only a $.10 -.20 per gallon spread.

[Quickurt]

I haven't, nor expect to, try this on my Boxster, as it is not a daily driver, I don't care what the gas costs. If I can't afford the premium, the car stays in the garage, but then again, maybe we'd just skip the evening out meal that costs a fill up of premium anyway.
But I digress.
I burn nearly three tanks per week in my daily driver, due to commute distance. It is a CX7 Mazda with 2.3 Turbo engine, 6 spd auto, FWD. Because of fill up frequency I think I rule out most of the questions regarding the previous post on 10 tanks, 10 tanks of premium/mid grade.
I have found very similar results on my CX7, doing 2 weeks of mid grade and back to two weeks of premium. 1125 miles of mid grade - 19.87 MPG, avg. $3.22- $0.1621 per mile. 1141 miles of premium - 21. 22 MPG, avg $3.32 - $0.1565 per mile. NOTE: less than 1 cent per mile difference!!
Again, this is NOT a Porsche, but verifies the previous test in a BMW, so it stands to reason it will also be so in the Porsche, to a similar degree.
Add to this, the car is SUPPOSED to get premium gas. Does it make sense to risk damage to your VERY expensive Porsche engine to THINK you're saving a couple of bucks, when, in fact, you are probably losing money on the proposition?