If 30% of the network are malicious, how many nodes would an SPV need to connect to, to be sure?
Under the assumption that the total node count is large enough that we don't have to care about the reduction of the ratio by only connecting to nodes we haven't connected to, yet: 

The chance to connect to five bad nodes in a row is 0.35 = 0.00243 = 0.243%. AFAIK, many SPV nodes only connect to 4 nodes, though. The probability then is 0.81%.