You say that as if it's easy for them to do that. A victory at Poiters may allow Muslim raiding to continue in earnest in Southern France but under no circumstances will it allow them further conquests. They were overextended and didn't have the Berbers to stabilize the border areas they would have taken. The HRE is just out of the question.
Exactly. But If France and the HRE(Or at least, huge chunks of it) are conquered, via help from intense use of wankium, Ireland would probably fall.
Never said it would be easy. Just used a lot less words.
EDIT: I think we need them past the Rhein, along with a foothold on the isles. Everything else depends on their internal stability.(Which i doubt would last, looking at the size of the empire)
On the other hand, the snowball effect should allow them to get just about the rest of Europe.