Although I haven't sailed an iS 133, I do sail formula. No the 133 will not plane as soon as a formula board, but the difference will be pretty small. At your weight, with a steady wind and good pumping skills, you could get the formula board on plane with a 10.0 in about 8 knots, but you will be limited to beam reaching. The 133 may require 10 knots (just a guess) to get going.
I have a friend with a hypersonic 133 and a 10.4. He weighs about 83kg and seems to be on plane nearly as much as me on a Formula board with an 11.0. I weigh 80kg.
I think the choice depends on your type of sailing. Formula if you race formula, 133 if you race slalom in light winds. If you just free sail, the 133 will be faster, but won't point as high or run as deep as the formula.
I don't think the early planing difference is very much. Choose by the style of sailing you prefer.
Both boards will take a lot of practice to maximize their potential. Neigher are designed for intermediate sailors, so you will have to be determined to practice, practice & practice. Both boards fully powered can be very very exciting to sail, especially if you work on deep down wind runs at speed.
The Futura 144 might be a better option since it is a little more user friendly and can handle a 10.0 sail.