can i use a synthetic blend

It don't matter. Unless u want it to last.. personally it don't matter because you'll end up throwing it away.. very temperamental engine. I prefer the 2.5 2.8 and the 3 l .... my m3 has 540k on it and going strong.. I've been using convention oil for 280 of them . Lol

Mobil 1 synthetic oil will give you superior protection. And, you can go 5,000 miles between changes.

Run full synthetic, should be good for 5,000 to 10,000 miles between changes. Pretty sure it has an oil life monitor. Refer to the owners manual for recommended oil change intervals.

Only use full synthetic. I would never put conventional in my 528. Just out of curiosity, Patrick, what year M3 do you have?