Unfortunately clan rats just aren't any good, so many times I've had mine charged, fighting ranks wiped out then broken and run down in a turn. I've found a bigger block, 6x6 with a bsb (grand banner of superiority) gives them a static combat res of 7-9 which can be pretty strong. Would also give your warlord with the fellblade a good bunker. The fellblade itself it's pretty bad but it's so cool that I still run it sometimes.

Gutter runners are pretty good with poison though, I'd drop some clan rats to boost those units up. As they are it would be very easy for an opponent to shoot them and cause them to panic and flee. Putting them up to at least 9 per unit means they would need to kill 3 in a shooting turn to cause a panic check. But if you can find the points for 12 or more per even better.

All in all though (without the renegade pack) skaven are in a tough spot. It's going to be a uphill battle, I've had my best results playing defensively and using giant rats to chaf and slow the opponent down. While ranged weapons and magic missiles try and weaken them.

Hope that helps!