This can help: http://docs.moodle.org/en/UTF-8_lang_files
section "The plan", point 2
There wil be a field unicodedb created, value 1, after the migration in mdl_config. I checked my 1.8 and it is there, I checked an unmigrated 1.6 and it has a unicodedb-field with an empty value in table mdl_config, field 1.
For English only sites, there is as far as I remember no iconv needed, but backup, backup, backup and test, test test!