It depends, I have had 8 people on our 23 for short periods of time. Last summer we were sailing in 25-30 knots with 8 on board and we did not feel unsafe. Bunch of people who were very into sailing I will add, can't remeber ever having more fun!
BIG HOWEVER, you must remember 8 people will outweigh the ballest you have below you. If your 8 people are willing to move around as needed and especially a few of them down low meaning below in the cabin as well as out on the rail, you can have alot of fun.
MAKE SURE YOU INSTRUCT them NOT TO RUN to one side to look at something, you have got to be on them about that at all times. When you tack make sure everybody knows there role and where they are to go as well as what they are to do. Lot of things moving on and above deck and 8 people make that difficult if they do not know there roles.
If you are motoring around, few people below, two up front on deck and one on each side of the mast will balance the weight nicely, BUT REMEMBER YOUR CREW HAS TO STAY PUT "for docking ect",
Life jackets, strict discipline, extreme leadership on your part and you should have alot of fun and remain safe. Loose control of that discipline and you will be in trouble.