Newc6--I follow your same logic and change my oil every 7,500. I do always use the BMW 5w30 synthetic as it is reasonably priced at $6 a quart and it really is the best choice for how the engine is designed.
Also, no more dipstick on BMW engines. This started with the introduction of the n52 inline 6 motor when the e90 was released.
Let me count the ways.....but first and foremost yes you should worry. I have 99k on my 09 x3 with the 100k mile maintenance plan. Do you know how many free oil changes I got? 5. Yikes!!! That's approx 19k miles between changes. No matter how good your oil is it isn't going to last that long.
As a side note there is a well know valve ticking problem that develops in these motors around 50k to 60k (n52)....I strongly believe this in part caused by too long duration between changes. Also my n52 is quite as a church mouse.
Here is a nice article that shows the head off of two inline 6 m54 motors...one changed every 7k miles the other as BMW suggests:
She was right. You can run 87 all day long with no ill impact to mpg, motor or fuel system. Performance differences are minor.
I am a super commuter and years ago I had a brand new 08 128 vert. I decided for 4 weeks I would run premium 91 and 4 weeks regular 87 all from chevron. It was spring so weather was a consistent temp in morning and night (California), driving conditions the same (80 miles each way at 80mph, 20 each way in stop and go) and I checked cold tire pressure every day.
Result -- there was less than a .3 mpg variance between 91 and 87 and no perceptible performance difference in normal driving.
Conclusion -- I have used 87 in all BMWs I have owned since. Like I said my 09 x3 has 99k miles on it no issues with mpg or fuel system so far...