Hi John,
Welcome to the forum - you'll probably get totally subjective feedback here!
I think when evaluating a P323 you need to be aware of what she is, and what she ain't. The P323 is a well-built, well-designed, moderately heavy coastal cruiser. Her weight and design makes for a seakindly movement which inspires confidence in heavy wind/weather. She is also surprisingly roomy for her size and age. However, these characteristics means she is no racer. As I am sure you know, in a boat it's all about tradeoffs.
Light air - there was another thread about that, can't find it for now - well, the P323 weighs ~13klbs, so she is heavy compared to many modern boats, and the speed will depend on your sail selection. Under 5 knot wind is a challenge - she won't make her own airflow like some boats near me! But as you get above 5 knots, I find she moves along fine - but perhaps I am patient?
Lines aft - well, that is a very subjective debate. Some P323 have their lines led aft, some don't. Some people think it is a big deal, others prefer the simplicity of lines forward. Personally I am wandering around the bow often enough that it is no big deal (I often singlehand). And I appreciate simplicity and ease of hauling on lines.
Upwind performance - well, if there is one thing which lets the boat down, it is upwind performance. Two factors come into play (IMHO) - the position of the jib leads/cars, and the shallow keel. Consequently, she does not point as well as, say, a modern Catalina, however hard I try. I take part in the local "beer can" races, and broad reach/running we move very well, and can keep up with or beat many modern boats of a similar size. But if we have to beat..well, it's not pretty, I must be honest.
As I said upfront, that's the penalty you pay for a stronger rig - and an older design. Sometimes it's a pain - other times it comes in useful, like when a month or so we went in to an anchorage and settled down, wondering why the other boats were waiting...an extra 2' on the keel helped them get there faster, but they had to wait for more tide to get in!
Have a look around this site, there have been other questions from potential owners; also have a look at
http://www.rollinscs.com/boatpages/choosepage.htm and
http://www.chessie.com/boat/, both of whom have excellent sites on their 323s, and participate in this group.
Good luck!