If you are mowing pasture I would go with a strait 30 , a 20W 40 or even a 20W 50.
The only reason for using a 10W 30 is if you are pushing snow or trying to start the mower early in the morning on a very cold day or are using a pull starter.
10W 30 is 10W oil with addatives to stop it thinning when hot.
So when cold it is very thin thus the small amount of smoke when cold