Naxx 10 is hard tbh, you need the players who know their class !
We were the first guild to do naxx 10 without stepping into naxx 25, but only with heroics and VOA gears.
We formed a great core for 10 man since those days of Naxxramas 10, and even in Ulduar i am pretty much pleased with our progress on Ulduar 10 being a social guild; {12/13 down }. Though we had a bit of help on Mimiron & Freya regarding tips only from our friends, rest encounters we did it on our own.
Since naxxaramas 10, our core has been :
Prot Pala / Prot War
Feral Tank
Ret Pala / OS Holy [Never had to be 2nd Hpala on any boss in 10 man naxx, so being OS prot will be a help as well on Patchwerk]
Frost DK / OS Tank [Tank spec having chillblains for kiting on Gluth]
2 MM Hunters
Shadow Priest / Disc OS
1 Mage / 1 Warlock [if your dk alone cant hold kiting on Gluth]
R Shaman / Ele OS
H pala
Only change done for ulduar was dropping mage/warlock for a Resto/Boomkin Duddu
The minimum time taken for Naxx 10 whole clear was 5 hour 30 mins for us, with some afk times, fun times, joking around on TS and yea tank pulling trash and going on bubble stuffs :D
Hope this composition helps you, and naxx 10 is really not impossible on i200, it just takes proper skills to do it.