The number with the w is oil's consistancy when cold, and the number after the dash is when it is hot. So 5w-30 will circulate faster when it is very cold out, but will exhibit the same molecular structure as 10w-30 when engine is at running temp. For most intents and purposes, there isn't a great difference. Unless you like to stomp on the gas as soon as you turn the key when the engine is completely dry. In which case, VTEC won't help you anyway (won't engage untill engine is at full running temp). I use 10w-30 Castrol Syntec. I prefer the peace of mind of a little thicker oil when cold, and I always wait till full running temp before I rev over 3000 rpm.