Ok so I'm reporting back as promised and I was able to play against both the Necron and Eldar players.
First game was against Necrons (I should specify that we play ITC comp and missions).
His army was roughly a Decurion with min tomb blades, 2x 10 man warriors, 10 Immortals, 2x Canoptek Harvests with min scarabs and 5 man Wraiths and a Destroyer cult.
I did get first turn and was able to knock out 5 Wraiths between the 2 squads and one of the Spyders. Essentially, the game was the Wraithknight got tied up by the Wraiths but ultimately dispatched them after 3 rounds of combat (I run the sword and shield variety). Dark Reapers did work on destroyers and ultimately I out ranged him to death. Final result, tabling by Turn 6.
Eldar bike spam army was a double CAD Autarch on bike, Farseer on bike, Wraithknight, 5 individual D-Cannons and I think 8 or 9 min scatbike squads and a couple of warp spider units.
He had first turn so I decided to reserve most of my stuff except for the the bunker w/ reapers and the D-Cannons. First turn wasn't so bad because he also reserved everything but the Knight, and D-Cannons. He was able to drop the void shield on the bunker with the Wraithknight but I was also able to scrape off 3 wounds with 1 volley of the Dark Reapers.
Turn 2 was critical as everything came in from both of our armies and he was able to take down the bunker and a couple of reapers, knocked out my D-Cannons. My stuff came in and I was able to wipe out in total 2-3 units of windriders as well as the Farseer and reduce the wraithknight to 1 wound. A lot of units were reduced to 1 man windriders and 1 man spiders. Turn 3 is where the army just really took it in the face and I had to tap since all venoms were destroyed all Avengers were destroyed as well.
So a couple of observations, while pretty effective, the dark reapers are pricey while insulated in a bunker. But they do throw out a scary number of shots it might make more sense to MSU them into little squads.
Archon + Wraithguard D-Scythes is good at eliminating a singular unit but afterwards is basically dead. Only really worthwhile if you anticipate Deathstars and are probably playing against comped Invis.
Sword and Shield Wraithknight is great but that Wraithcannon really does make a difference. I'm on the fence still.
Army needs work for sure, but against these armies my hope of playing a pure Dark Eldar force may require ultra venom spam or something.