Synthetic oil is far better than the others. Use AMSOIL, change yearly.
If you don't, or won't, use AMSOIL, then Mobil 1 is an excellent second choice--go for the new extended drain 15,000 mile oil in 5W-30 or 10W-30.

Made in Japans' got it right. I just want to add a few pointers because I've been doing this since 1968.

Try to get the oil nice and hot before you drain it. It'll flow easier and you'll get a little more of the bad stuff out. And let it drain for 10-15 mins before you replace the drain plug.

I always fill the new filter up with fresh oil before I screw it on. Hand tighten it and then one little tug with filter wrench should do it.

I have the turbo and I use synthetic (Mobil or Castrol)in a 5w-30 throughout the cold season. In the warmer months I use 3 qts of the 5w30 and 3 qts of the 10w30. Actually the syn lasts up to 10k, but 6k is OK

I use the NAPA Gold filter because it's made by WIX. Mann makes decent stuff too. Good luck

You are a little south of Minnesota, so 10W30 will work fine all year. Synthetic if you have a turbo. You can buy Mann filters and crush washers from FCPGroton or IPD by the case.

Klaus
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98 V70Rawd(108Kmi), 95 854T(88K mi), 75 164E(173K mi)

Do you have a turbo? If so, then full synthetic is the best choice. Otherwise, it's one half dozen or the other...just change the oil every 3000 miles as recommended. If you have full synthetic (ie: Mobil-1) you can go twice that.
As far as viscosity, I go with 10W-30 in the fall and winter and when it starts to warm up outside in mid to late spring, I switch to 10W-40, but that depends on where you live too...I live in S.E. U.S. Most all information of this nature is in your owners' manual.

I'm sure there are all different opinions here in regards to oil maintenance including the guy (Breadboy it is?) with almost 400,000 on his 850 who's oil usage and type, etc., seems to have been haphazard during the life of his car. Main thing is to keep the oil changed before it has a chance to break down.

My S70 (I assume it's the same quantity as your 850 but check your owners' manual) is just over 6 quarts (without draining the oil cooler which is a pain and not much comes out anyway so I leave it alone), so tighten the oil pan nut and oil filter and then fill with 6, check everything and then top off as needed.
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1998 S70 T5 Emarald Green Metallic, 2004 V70 2.5T Ruby Red, Previous Owner of Black '94 850 Turbo Wagon