High Elves conversions

I posted my Ynnari project down in the Project Logs ( http://www.thedarkcity.net/t15916-the-legacy-grasped-reborn-warhost ) and been thinking about conversing some High Elves models as they feet the "Aledari returend to glory" feel of my army much more than any Dark Elves (except maybe Sisters of Slaughter for Banshees, as I dislike their finecast counterparts).

I have a question for more competetive oriented players - how heavily conversed should a model be to pass as a unit? Right now, I was thinking about conversing Swordmasters into Incubi by swapping helmets, as their clean look fits the whole army vibe much better, but will it be enough?
Same question about the Prince on a Gryphon - I was gonna use him as a Farseer on a Windrider, as the model already has a pretty nifty spear that would make for a swell Singing Spear. The model is realy nice and it would be a shame to overconverse it, so from a tournament perspecitve, if I fit Wysiwyg by adding the Ghosthelm and some eldar weapons onto the Gryphon, would it pass? And is size any problem? The model is way bigger than a Windrider.

I think that there should be no issue with any model as long as it is clear what is what and keeps within marginal size difference. So Swordmasters as Incubi are perfectly fine IMO.
Griffon as jetbike on the other hand is way too big. In 8th the size of the model is largely irrelevant, especially when using bigger models is detrimental to you and not the opponent, but I would not allow it and most players I know either outside some very friendly game. It looks weird too when space dudes shoot griffons and griffon spits shurikens.

But I myself plan to use multiple High Elves parts in my Ynnari. But not whole models. Spear is great...