This is a timely thread. I have an 'itch' for a Sako and have been asking some questions/gathering info. From what I have gathered, the 75's are heavier than the 85's. The 85's have an 'enhanced' magazine release which prevents accidental removal, whereas the 75's do not. There may be other differences that i overlooked or am not aware of.
I dont have a Finnlight but I have several m75 SS and Greywolf rifles. IMO, the accidental release has never happened for me. My first Sako m75ss rifle was new back in 1997. I know it has happened but IMO,its more of a gimmick upgrade.
I personally prefer the m75 stock design over the m85. I guess you can always get a MacMillan stock in the m75 design for a m85 rifle. That might be something to consider, getting a used m75ss or Finnlight and ordering a MacMillan Edge or standard stock.
I also do not care for the factory fluting on the barrel compared to the custom fluting by a gunsmith. I have had 2 factory barrels fluted on my Sako m75 rifles.
