That's usually the case with anything that needs motor oil. The thinner the weight the easier it is for the components to move. The thicker the weight the more it protects the motor but at the same time that harder it is for the components to move.
Been changing mine annually on the same 8 hp Tecumseh for over 30 years with no problem.
I used 10W-30 for a long time and switched to 5W-30 about 4 years ago.
Regular Quaker State has worked fine for me. I do think any major, well known brand of oil that meets the API SJ rating or higher will work just fine. I think the API ratings now go to SL and SM.
The later letter in the alphabet denotes the later or newer release.
Tecumseh recommends SAE 5W30 for my old 8HP L head, and I believe B&S also recommends the same for winter use. If I recall the recommend changing evey 25 hours, but I don't put that much on in a season, so after the season is don, it gets fresh oil. I don't use synth, but I do think that any reputable oil will do.
Well... Im REAL bad with oilchanges on my snowblower!! I think I went 5 years before without changing it. That being said... I would change it once at the end of the season. that way you get all the water, and acids out of the crankcase before it goes into its long summer slumber. For oil I ALWAYS use synth oil in my snowblowers. It cost more, ya... but realy you only need a qt or two once a year..It makes starting in the cold a LOT nicer!! Also holds up well to the heavy load a snowblower lives with.