RE: EVO 83 or 91
While I'm much ligher myself, I still belive the E83 is useable with a 5.8 in 18 knots at 91 kilos. It will definitely be a low volume solution and you will notice this at standstill for sure. But once going (even below planing) and especially on a wave, you will notice the E83 is very, very efficient. The E91 will surely be a far better board for 5.8 conditions, but it will also be harder to handle and feel less natural once you're powered up.
But as an all round wave board, I think the E83 will be it. I think it will blow you away in powered up 5.4 and in 4,7 conditions and handle the 5.8 noticeable better than the F2, I think. If you're sailing lots of 18-20 knot sailing and are willing to make performance in these conditions a big priority, the 91 is it. Even at my sub 70 kilos its possible to handle with a 5.0 so I don't think you will have too much aof a hard time of it with a 4.7.