Its simple, it revs and responds to the clutch quicker and has a more aggressive feel. You can also fine tune it with the spin on weights. The "3" just gives the bike a bit too much of a lazy feel, good in the real slick technical stuff but not elsewhere, especially on a 200. Also note that the '12 has a full circle 10 - 12 oz weight behind the primary pinion(from 8 oz eccentric), so the end result is not like a stock YZ. This is JMO.
The 200 might have lighter springs than the 250/300, as I'm just under 180 and the stock springs on the 250 are not bad. Only on the MX sections do think of heavier springs.