Definately now

newer gear is generally easier to sail on the old gear - but how old are we talking?

4.7 is quite small .. im only 65 and my 4.2 rarely come out id suggest u go for more like a 5m-6.5m

Depends what you want and on your style.

Older sails have more power for their size because they are deeper and tighter-leached, therefore creating more lift but more drag.

In return for extra lift (power) they are harder to handle at the top end of the range, and the extra drag means that they are slower at the top end of the range and don't go upwind as well.

Older sails (in my humble opinion) can be faster in gusty conditions, because you can power up so quickly compared to a similar size (and weight) modern sail. But you'll definitely lose out in top speed when fully powered, and in upwind ability in a breeze.

A modern sail as big as your older sails may therefore not replace your old sail, but actually be better for stronger winds and (IMHO) not so good in lighter stuff.

Many sails tend to be designed for open-water conditions and at high speed because that's where and how pros sail, which means that they may not be optimised for "normal" conditions where most of us sail - IMHO.

if getting a newer sail, grab a good mast as well if you have a real oldy. what mast are you using at the moment?

the twist on a sail is enhanced with the correct mast. like a fibreglass mast compared to a skinny 100% carbon job, or even a low carbon compared to a high carbon mast.
the newer sails are so much more forgiving when rigged correctly.

...exactly why I said "dont know the details of your kit" at the beginning of my message

and as I mentioned what I am saying only applies to a reasonably modern sail...

If his sail is that old should probably consider buying both, but neither has to be new. can get decent sail for under $300 on the classifieds..

Al