Regarding the firmwares, generally all the variants with numbers 200 or higher are for operators, so in principle you always run the risk to get a 'branded' version (although, some operators are more discreet and don't put their logo everywhere).
So, probably it would be better for you to have a good look at the list of variants available, sort them by increasing variant number, and try them one by one, starting from lowest number.
When you find one that seems decent, be happy, otherwise go on flashing the next one in the list.