ISM Shortwave Transmitter

Greetings all from the UK

I read the following post with interest about a shortwave transmitter

http://www.part15.us/forum/part15-forums/transmitter-talk/ism-shortwave-transmitter-continued

My question is what kind of range have users in the USA managed to get?

I too can use this transmitter in the UK but ofcom state that the power output should be no more than

42 dBμA/m at 10 m

Could this number be converted to a mW power limit and if so what would that roughly be?

Or is there an estimate of range that a signal of 42 dBμA/m at 10 m would give?

Any insight would be greatly appreciated

Cheers