RE: EVO recommendations..
Since I only weight 150 lbs its a bit hard for me to predict exactly how the boards will work for you. I had the 90 and have the 80 now (+ the smller EVOs - the 80 is my light winder). Even for me, the 90 works nicely in powered up 5.3 conditions (but 5,3 for me would mean less wind than for you). I think it stays loose also when powered up, but the size makes it less good when it comes to handle chop for me, but with 50 lbs extra to put in, I'm sure this will not be a problem for you.
As for the 80, no doubt it will feel smaller overall and you will have a much harder time schogging through he impact zone in super light winds. But once on a wave, it will still be very effective accelerating and keeping speed and the better (faster) the wave is, the better it will go. Note that the 80 has a very wide tail, so even if you do loose speed a bit on a wave, it will not sink on you.
So again, its very hard to choose between these two. Generally, to get max all round performance from the EVOs you tend to go down a bit in volume compared to a traditional board. In the end it probably comes down to how much light wind comfort you're willing to trade for extra performance on the wave in good conditions. One way to phrase my recommendation would be to look at speed on the wave. The faster you go the more I would lean towards the 80. The team guys like Scott McK are able to generate lots of speed in pretty much all conditions and hence they are typically on very small boards for their weight.
So, both boards will work - which one you get is a matter of "tuning" your equipment to your style and competence.
Fins: You can consider the original fins as pure high wind fins for you. I doubt you will even need a smaller fin than the 24 on the 90. These fins sail very small for their size. I would complement with a 26cm Drake Natural for the light wind and onshore days. This seems huge for a wave fin, but it actually works very good.
Onshore: The EVOs have quite a lot of rocker and don't have the feel of "instant planing" that many fast rockered wave or freestyle wave boards have (Acid, Kombat). But the difference can easily be overcome with a bigger fin and some more work from the sailor. You more loose a bit of that relaxed "gliding along" feel of a fast rockered board in light winds than you loose actual planing performance. And getting through white water is very easy on the EVOs. If you want to ride wave (frontside) also in onshore or cross onshore conditions, the EVOs are just remarkable since they simply turn much better at slower speeds than its faster rockered cousins. The 90 has a bit rounder outline and will be even looser in slower onshore stuff, but the 80 is great too. I sailed powered up 4.5 cross on the other day on the Acid 74 and had a great time. Perfect size for the conditions and very nice working board. But then my wife sailed for a while on the EVO 80 and later I just grabbed that rig. And despite the 80 being kind of big for the conditions for me, there was an instant improvement in the wave riding. This is the key point of the EVOs. If performance on a wave matters, there are not many other boards that can match them. And the versatility on a wave makes them very tolerant when it comes to which size you're on. The "80 day" above I could have had just as much fun on the 62.