very novice part swapping question...

[abejita]

Ok, I've only been cycling since last summer and this is my first attempt at minor upgrades on my bike and would like advice.

I have a friend who upgraded his cassette and crank and gave me the parts he replaced. I have all 105 components on my bike except for a FSA crank. I would like to swap out his cassette with mine because it would give me an extra gear to help on the hills. His cassette is 12-27T and mine is 11-25T. They are both 105 cassettes so I don't forsee and issues with this.

My question really more concerns my husband's bike. He has sora/tiagra mix on his bike. He wants to put my 105 11-25T cassette on his bike and a FSA Gossamer crank on his bike. The problem is that his bike is 9 speed. I am not sure that these new parts are compatible and if there will even be increased performance from these parts if he can use them. Any opinions?