(1) Yes, IBR allows you to pay less per month but in the long term, you will be paying a lot more interest. Your payment will not be much within the first couple of years but after you have earned a full pharmacist salary, your monthly payment will jump.
(2) I don't know where you are getting this, "IBR payment will rarely exceed 900-1200 per month at our income level". You know as your salary goes up, your payment also goes up right? You know if you married to someone who doesn't have student loans and also makes a good income, your monthly payment will jump right?
(3) I also don't know where you are getting this, "(IBR) represents a small percentage of the total net income". You are obligated to pay 15% x [adjusted gross income (for most people it is pre-taxed salary - 401 k contribution) - poverty line] with your
after taxed ("take home") salary. For example if your adjusted gross income is 100 k, take 100 k - 12 k (poverty line for single adult) = 88 k then take 88 k x 0.15 = 13.2 k a year. If you live in a state like California where there is also a state income tax and after health insurances/dental, your take home salary is about 65% of what you make so that's 65 k. Lets see 13.2 k/65 k = 20% of your take home salary every month for the next 25 years!
(4) Whatever student loan that is left over after 25 years, you would have to pay tax on it. Expect to pay around 25-30% tax so if 100 k is "forgiven", you would pay 25-30 k in taxes
IRB is an option for people who can't afford the 10 year standard plan but in the long run, you will be paying a lot more interest. Here're some numbers based on 200 k in student loans, 6.8% interest rate, starting annual income is 120 k with an increase of 2% annually:
http://www.finaid.org/calculators/ibr.phtml
(1) 10 year plan: total paid $276 k (76 k is from interest)
(2) 25 year IBR: total paid $394 k (194 k is from interest; yes, almost 100% of your original principle of 200k).
As you can see, you will be paying a lot more money with the 25 year IBR and guess what? there won't be any thing left over to be "forgiven" after 25 years! Yup, you will be paying the original principle plus 25 years of interest!