Considering Karoo charge an additional £1 per GB, after your reach your 150GB limit on the highest Karoo BB package, something tells me your not downloading that much whatsoever.
Unless your paying Karoo an extra £50-150 a month, just to download. Although o'course, you could be doing all your doing all of your download between midnight-8am.
You must have to buy new data storage on a regular basis just to keep up with your downloading!
Max is unlimited 8am to 6pm...