Question, you want us doing rolls in the IC thread or OOC thread?
Also, are you taking the decreasing dicepool for extended test option?
If not, everyone can succeed in any extended test, if enough time given.
If you want to limit it by skill, its the suggested way of the book to reduce the dicepool by a cumulative -1 for each following test.
I.e. with a dicepool of 16 and buying hits, i could buy 4 in the first test, 3 in the next 4 tests, 2 in the next 4 tests, and 1 in the last 4 tests, and be limited to a max 28 hits in 13 tests total.