I don't know how it will affect your score but my experience is the same as brownsugav in that while my loans were in forbearance or deferment they never reported as closed. In fact, the months where I was in deferment are blank on my credit report.
Keep in mind that your scores are already good. I know with student loans at over 100% you can still get over 750 credit score and when the baddies come off (2012? You could always try to have it removed up to 6 months early with early exclusion on TU) potentially near 800. I wouldn't worry about it too much.
One thing I did notice is you were on forbearance while you were on a IBR. Are you planning on repaying the whole loan or forgiveness? If you are planning on any forgiveness, I recommend avoiding any further forbearance or deferment even while in school (you'll need to complete an in-school deferment waiver) because all those payments will count toward the time needed for forgiveness. Hope this helps. :-)
