Correct me if I am wrong but it seems to me that manual updates are only executable on a PC as aside from everything you are all saying (and not saying) the v.585 download from RIM's website is a PC only file that did not run correctly on my Mac.
I suppose the OP's question has been answered by now, but just my 2 cents:
I used to shrink my OSs when I had my 9700, but have found it is not so much needed with the additional specs the 9900 has.
I've been on .540 for some time now and have experienced no issues. The battery life is terrific and it is rock solid - I can't remember the last time I did a battery pull.
This being said, I agree with many other posters that one version that works well may not work well for another, so it's mostly a matter of individual trial and error.
