Ah sorry missed the earlier question as jay said it all depends on which CF card you get, I will go into it a bit now just for reference but in terms of price/performance unless silence is required or you can not fit a normal HDD, the HDD is pretty much the best option.
For the CF cards to be any good you really need a fast card we are talking 133x at least but 300x as a preference the problem is a 4GB 300x card is £35, so you can imagine the costs of a 16GB card! In fact fro the money you could probably buy a 32GB OCZ SSD which will have better performance than the CF card as well.
Basically the cards cost to much so HDD are better, sad but true.