yes, yes yes, rate DOES matter - it makes all the difference! I got horrible aseptic meningitis my first loading dose- they ran at 205.... they threatened to take it away from me as well, but we tried again at a lower rate.. when we would hit 70, i felt the head pain start and even had a bit of chest pain too... for the longest time we could never exceed 70... slowly, after months and months we increased the rate to now 100 (i've been doing this for 3 years now)..
We also switched brands to gammunex, which is considered to be a "cleaner" ivig, therefore less reactions...

For me, the rate we increase the rate (at the beginning of the infusion, it is standard for my infusion company to go up every 15 minutes until you hit your max rate.. we do every 30 for me.. makes a big difference)

that, and tons of water! Good luck!