That's not how it works. You have to deduct armor soak from each hit, so it's less, way less.
6 pt with 170 wpf vs someone with 70 armour value:
Pierce 60:
Minimum: 28.47
Real Average: 31.94
Maximum: 35.58
Raw Damage: 100.18
_________________
Pierce 47:
Minimum: 20.08
Real Average: 22.85
Maximum: 25.74
Raw Damage: 79.25
_________________
Now lets compare them multiplied by the number of lances.
Min:
Pierce 47: 20.08x6 = 120.48
Pierce 60: 28.47x4 = 113.88
Ave:
Pierce 47: 22.85x6 = 137.1
Pierce 60: 31.94x4 = 127.76
Max:
Pierce 47: 25.74x6 = 154.44
Pierce 60: 35.58x4 = 142.32
Raw:
Pierce 47: 79.25x6 = 475.5
Pierce 60: 100.18x4 = 400.72
All results have been rendered and found by using this damage calculator:
https://0b176db51ec327b013e6b005fde2cca145eb9267.googledrive.com/host/0Bzs1vJv0tQLHZ3AwLUQ0Tkt0djg/calc.htmland Microsoft Calculator.
The evidence above show that 6 lances with 47 pierce deal more damage in every aspect than 4 lances with 60 pierce. If anyone would like to replicate my results. Simply enter 6 pt with 170 wpf vs an armour value of 70 and the stats for 47 pierce and 60 pierce will be as shown. I then multiplied the value by the max number of lances to show clearly what a dedicated lance thrower could do one way or the other.