I understand your hesitance with going to Gen4 because of the increased data you can get with your current plan. I had that in mind when I wasn't upgrading, as well. Then I thought...do I stay up every night and use my computer for five hours? The answer was no. I could get more data with my current plan, but I never, EVER came close to using it.
Twice during upgrading my computers to 8.1 it didn't work because it didn't finish in the five hour download zone and I didn't have enough free tokens to cover it afterward.