For me, at least 40% IF we beat Chelsea. That might be the more difficult game. Chelsea aren't as bad as their recent results may suggest.
We may fail to win every game, but Arsenal are likely to drop points too.
They tend to struggle after European games. If they eliminate Sporting, 3 of their last 6 games will be after CL games: City away, Fulham (h) and W Ham away. They don't look fresh, and that's probably normal, given they have been in a title race 4 seasons in a row.
On the other hand, we tend to hit form in the final months of every season under Pep. Few defences can look solid against our current front 4.