what is the best oil to use in my 06 yz 250f, 06 yz 450f in 60-80 degree weather. i do approx 2 - 20min motos, 2-3 sprints, then practice on corner track for about an hour every day five days a week. we change oil every day and the filter every other day. should i be using a synthetic, blend, or reg, and what weight?