After a period of rapid expansion, I have outgrown my shared hosting at Pair Networks, and am moving to my first dedicated server.

I have about six low-traffic web sites, two medium-traffic, and one forum (Invision) that is kicking me in the pants.

Thanks to the success of some recent magazine advertising, the forum has maxed Pair's database restrictions and is offline for half the day because of the demand. I'm not mad at Pair, as they have given me nothing but fantastic service for the three years or so I've been with them, which is why I'm going to one of their dedicated boxes.

So now that you have the background, here's my question -- how much traffic should the dedicated box be able to handle? Mostly I'm worried about the forum since the other sites are comparatively benign. I know that Invision, like most fora, is a MYSQL hog. How many users should I be able to sustain simultaneously? Right now it seems to hit Pair's max_connections limit if there are more than 500 in a 90-minute period.

The reason I ask is that I'm trying to plan for future server needs, and the possibility of eventually going colo, should the need arise. I don't want to be caught by surprise again and have my site offline due to high traffic. I'd rather relocate to my next box long before that happens.