Hi Cookie8,
I had a 5mW before it died and now have a 10mW. Although I was never able to compare them side by side, I can say that there is a noticable difference in strength. I live in suburban Ashfield, so its closer to the city than BH.
The beam appeared thicker and the dot more visible.
One thing I will add though and by putting in fresh batteries also makes a difference. I don't bother with the akaline batteries, I just used re-chargeable NiMH and don't have any issues with them.
Finally the 5mW was an el cheapo from Ebay which worked fine for a short while, but just gave me grief. I purchased the 10mW from Bintel and it works 1st time, every time.
I just have a gut feeling these things are going to be banned in the not too distant future with morons shining them at aircrafts/chopters etc.