I can't guarantee how long the stories are by the number of words, because I get mine from various sites and it doesn't state how long they are, but here are a few that I love:
If You're Not The One by KogasAngel (she's filled with awesomeness)
inu.adultfanfiction.net/story.php?no=544185355
A Question of Honor by KogasAngel
inu.adultfanfiction.net/story.php?no=544204706
Something To Talk About by KogasAngel
inu.adultfanfiction.net/story.php?no=544206585
Taisho's Darlings by Lavander Valentine (<---this one is 151,487 words)
www.fanfiction.net/s/1774880/1/Taishos_Darling
A Cross of Blades by Striking Falcon (228945 words)
sesskag.dokuga.com/fanficread.php?fid=1200&cid=1
My Experiment by Shasdowsweaver1 (this one is 116,692 words)
sesskag.dokuga.com/fanficread.php?fid=5054&cid=1
Tears of the Fallen by Shadowsweaver1
sesskag.dokuga.com/fanficread.php?fid=5397&cid=1
Winds of Change by KogasAngel
sesskag.dokuga.com/fanficread.php?fid=1876&cid=1
As Death Gives Us Life by Rinseternalsoul
sesskag.dokuga.com/fanficread.php?fid=2865&cid=1
A Sister's Gift by Rinseternalsoul (this one is about 90,000 words)
sesskag.dokuga.com/fanficread.php?fid=2126&cid=1
Unworthy One By Vyncent (This one is complete, she has another one called You Darkness that is a wonderful, yet dark story, it leans more to Inu/Kagome but there is quite a bit of Sesshoumaru in it too)
inu.adultfanfiction.net/story.php?no=38138 (<-Unworthy One)
*Sniffles* I miss Vyncent!
I have a lot more too...some of them are the Single Spark links...I think most of them have Dokuga counterparts, but its easier for me to read and turn off page styles there...my vision sucks, lol. ALL of the authors are awesome though!