70wt? That's pretty thick/stiff. I run 45wt. in my nitro savage which is pretty heavy and it is pretty stiff. i have been told 25wt. or 30wt. is good for racing (or little or no jumping etc.)
on my savage with 8 stock shocks i used 25wt and jumped it high and stuff and it worked great. if you get really thick stuff your gonna need really! strong springs. For 4 shocks i would try 40wt?