I've prev had a high powered green laser for a rifle. It was rated at 5mW, but the chinese lasers are known to be mislabeled. I beleive it was more powerful than what it was labeled to be. The thing was TOO bright. It lit up an entire room, and it would shine over 100 yards in bright sunlight. Easily over 1000 yards at night.
It actually hurt my eyes to look at it on the wall if I was closer than 7-8 yards.
I found it to be not safe because it would reflect too easily off of shiney objects - not mirrors but vases with a glaze on them, and anything even remotely shiney. I had it cross my vision path more than once this way.
I did a lot of reading online (this was in 2007), and found out the problems with these cheap green lasers being so powerful.
I decided that it wasn't worth having.It wasn't worth messing up my vision, even when I was trying to be careful with it.
So, be careful - if you get something that powerful, you better get some safety glasses made for laser light.
Isn't there a sponsor here on the forum - Wicked Lasers or something like that? I saw a banner a few days ago. I cruised their website, and they have some VERY powerful lasers. Just refresh the sight a few times in your browser window, and you should eventually see their banner.
Honestly - I think it's a mistake to buy a laser powerful enough to do what you want just to play around with.