You need not fear. You will still get by with only one board. A modern classic like the Pure Acid 74 if anything has a bigger range of both sail sizes and conditions it can handle than older boards. 4.0-5.3 is just the sweet spot for that board at your weight I weight about the same). I would say an EVO 70 has a similar range. But while the EVO 70 also handles the conditions you describe and is preferred in such conditions by some people, I think that the Pure Acid 74 is the natural choice.
To elaborate a bit more on the differences, the PA74 is a very effective shape, fast and early planing. On a wave it has a fantastically secure bottom turn that is very confidence inspiring in bigger waves. It has a sharp and direct ride, but still confidenly cuts through chop. On a smaller wave, it still prefers a kind of front foot oriented turn and it need a bit of technique and commitment to go vertical when waves are small. But if its reasonable close to sideshore, the PA74 is still rather easy to rip on also in small waves.
The EVO 70 conversely practically rips by itself in smaller waves and goes vert like on autopilot. It handles big and fast stuff too, but the faster it gets, the more you need technique and commitment to pin it down in the bottom turn. Its not like its misbehaving or anything, but it needs a certain kind of turn setup to settle in the bottom turn. An EVO does not feel so "sharp" in the bottom turn but it actually hold an edge excellently. Approaching the top turn, it still like to go vert also in big waves.
So, if you have the technique (or are willing to work on it a bit) both boards work just as good in everything - just with a different style and with a different kind of feedback. But if you maybe have a less adaptive technique, an Acid will help you out more in bigger waves but be more work in smaller and an EVO will help you out more in smaller waves but be more work in bigger waves.
I hope this explains things a bit.