I haven't sailed the ET87 nor the ET80, so its hard to say exactly how they would work for someone our weight (I'm 70 so rather close to you). The ET 74 planes fairly early though and the ET80 has a faster rocker and is wider so it should go a fair bit earlier and the ET87 maybe a bit earlier still.
I don't think you need to worry about the gap to the E70 becoming to large even if you go for the ET87. The E70 is a versatile board and works really well all the way from powered up 5.3. Its only when you need the volume or prefer some more width to drive the turn on that a bigger board is needed. And of course when you just want "more board" for light/gusty onshore.
So as I see it you are pretty much free to choose E80, ET80 or ET 87. The question is only to find the board who will handle your light wind duties the best. All are riding oriented and since the ETs are based on EVOs they are rather similar in overall feel. But the ETs have narrower tails and, of course, twin fins. They will be comparatively easier to get on their rails and easier in the top turn relative their size. On my ET74, upwind (also in marginal conditions) is very good too and there is no reason to believe this should not hold for bigger ETs.
But I still think the E80, especially with a bigger fin, can be trimmed for better onshore/B&J performance. It has evolved over the years and is now a rather crisp feeling board with a huge range. But if you're not so worried by this straight line drive, an ET would make a great big board.
And maybe the 87 would be the best. But I would still think about if the ET80 is not big enough? At your weight it will surely carry 5.7 well and I think that if you sometimes sail more B&J like conditions you might wanna put on a bigger sail (relative the wind) to get some more drive. This might be easier to on the smaller ET80. So in such conditions you might in fact be able to get more straight line drive out of the ET80. What do you think?
Edit: What I personally found from using EVO 80, 90 and 100 is that while there are times when extra volume of the 90 is nice, it does not really translate to earlier planing for me. And in onshore stuff, the board gets a handful when you get powered up and you need to be careful with fin size to be able to handle it. With the E80, you can go for a bigger fin and a bigger (or more powerful set) sail and get a better blasting board. This is the background for the last paragraph above, but I can't say for sure how it relates to ET80/87.
Last edited by Ola_H; 1st September 2008 at 04:20 PM.