According to that spreadsheet I should get ~47BTC with the free upgrade and ~130 with the paid, which costs me 46BTC.

So if I go with the paid one I'll have 84BTC more at the end of the 9 months, vs. the 47BTC of the free upgrade

The problem here is that we have to decide being blind, because we don't know when or if this is going to begin, but in case we choose the paid upgrade, we have to pay the BTC on the following 5 days