Re: D&D 3.5 High Powered / Fast Progression
Granted, with a group of 4 or 5, there's likely some overlap between the PCs, such as there might be multiple clerics, though they might vary in the roles of casting/turning/combat. As I've heard said, pick something and do it really well, but don't overspecialize.
On the other side of things, if a player's ready to take the initiative to learn the relevant rules and get their PC built in a timely manner, I'm not too terribly concerned about whether this is their first time playing or their 5000th. YMMV. :)