Hi i'm planning to buy one of these quality machines, i'm stuck at whether to get the medium 2.5 inch diameter or 3.5 inch large one, for those who own a 2.5 inch grinder, is it big enough to grind a lot of herb? enough to grind 1/8 at once? or should i opt for the large one? i've nailed down the exact grinder all i need is advice on either medium or large, i like medium although im afraid it may be too small? i will be taking it out, (in a bag, not in my pockets). Also i'm sure this has been asked before, but if i grind up 1/8 of an ounce every fortnight, how long till i have a 'significent' amount of kief?