I still think its just silly having 2 different named 'standards' when indeed they are the same thing, one just being a little more 'exotic' than the other.
Not really different 'standards', just Shimano offering a range of different price points/levels like they do with most components. The ones with higher number will (normally) use better materials and be lighter, but also cost more. So, in press-fit MTB BBs they offer three choices - BB51 which is Deore level, BB71 which is SLX/XT level, and BB91 which is XTR level. They are interchangeable, so its your choice...
I'll probably get it installed by a bike shop anyway since it will be part of the overhaul
All I can say is choose your LBS carefully. I do all my own maintenance because frankly, I can do it better than the muppets in my LBS (and lots of other reasons like I enjoy it, and I want to know how to do it for when it breaks in the middle of nowhere). For example, when wanting to change a press-fit BB for the first time I asked my LBS if they could do it. The answer was an enthusiastic yes. I then asked in an innocent way if I could see the special tool they'd use cos I've never seen one before - and you've guessed it, they didn't have the tools. Having been burnt like this once before - when I asked them to face a BB shell, to then watch in horror as they set to it with a file, this time I decided to invest $50 in getting the tools and doing the job myself. Of course, there are good and bad LBS like everything in life, and you may be lucky to live near a good one...
