Cannot get interface speed with standard MIB, use highperf mib (-g)
This has nothing to deal with MIB. The message you get means that your interface in question uses 64-bit counters, and those are not enabled by default in check_snmp_int.pl or check_netint.pl.
As the error message suggests, you should add '-g -2' to check_snmp_int.pl command line definition under commands.cfg.