if you go with feet shoulder width,at least break parallel you should be feeling your quads screamin',and a couple days later you will still feel it,you could try going 10,8,6,4 .........it's not that you want to just concentrate on going to failure,you want to keep a log of the weight and reps so you keep adding weight every week and you will get tyo a point where you will go for the 8 reps and only can do 7,stay at that weight till you get 8.... and so on..........