I gotta admit it. I'd take two mortars against this. You can scatter by 10" and still hit spot-on a unit of rats!
Yep, I'd take a Hellblaster too.
But how are detachments going to work? You won't ever get a counter-charge off due to the fact that there is just another block of rats blocking your charge arc. In any game, I rarely get a counter-charge against skaven. I think it quite impossible to get one off against this army.
Atchman, I would keep my big block of Knights at home too. You have this monster uber-unit that can toss aside anything the rats throw at it, and that's great, BUT what if the skaven general wisely places reserve units directly behind forward units? Your Knights charge and win by a ton, the rats break-- now what? If you pursue, you'll run smack into another unit and they'll have their cousins in another blocks salivating because they're going to flank you on both sides because it's their turn next! If you don't pursue, you'll get charged by none other than the unit you were going to pursue into. Which is what I'd actually favor simply because it beats getting flanked, but you're still in a bad spot. Can you work your way out of it? Absolutely. Is it worth the gamble of the amount of points you could lose in that one unit? I don't think so.
As I said in the Email. I think I would go with what you personally recommended Vincent of Vega do against Brets. Bring the following:
1 Unit of Greatswords - Griffon Banner
1 Unit of 30 Spears - BSB Banner of Sigismund
1 Unit of Flagellents - preferrably 20
Put them all relatively close to one another, and now you have a battle line with one unbreakable unit, and two with stubborn rerolls! Let the rats run their heads into that brick wall! Then just grind them down once they've engaged. Send in other infantry for support, and try to tip the scales of battle.
I'd also use an Elector Count and have him close by so the stubborn units won't easily panic if they get flanked.
I'd use my last two hero slots for 2 lvl2 Heavens mages and let them go ratling gun sniping.
If the skaven have a BSB, I'd mortar the tar out of his unit. There is a pretty good chance the BSB is holding the Sacred Standard of the Horned Rat (unit causes fear.) That sort of thing makes stubborn meaningless. If he jumps to another unit, I'd blast that one then. One unit of 30 of clanrats causing fear could roll up your entire line if the Skaven general gets his way.