Really depends on where you are setting your stoplosses. If you set your stoplosses at for example $8001,- a 1 dollar spread is probably enough beceause there should be laying a shit ton on $8000,-. But if you are setting you stoploss for example on $7999,- you better set a spread of atleast $30,- if you want to be almost 100% sure your order gets filled (because the momentum/stoplosses triggered when going trough such an important support most of the times will push the price significantly lower in 1 instant without filling any of your sell orders if set to tight).