I've been on a 305S that was use by a school and for occasional racing. The boat I was on had running backstays (I don't know if this is standard or not) but you may want to consider this if you are sailing as a family and don't want the extra work or do not have enough hands to manage them. Apart from that the boat should be fine for what you are looking for - they can hold their own in racing in a cruising boat class.
I think that the First range of Beneteaus in the mid 80's, when the 305 was built was the best boats they've built. The 305 has a practical cockpit, a comfortable interior and good though not frightening performance. They came in various flavours, a racing version which has a larger rig, a cruising fin keeled version which is by far the most popular in the UK and a twin rudder, lifting keel version which you'd need to go to France to buy. Also have a gander at one of its rivals, the Jeanneau Sunlight which I sailed for 12 years with 2 young daughters, though I think the 305 will sail quicker.