Considering the schedules that Barcelona and Real Madrid have before the El Clasico match, it seems that Barcelona is in a more difficult situation. Because after all, Barcelona will play against Bayern Munich, while Real Madrid will play against Dortmund but, in the El Clasico match later Barcelona will play away and also Barcelona will have less rest time compared to Real Madrid. With these differences, Real Madrid should have better planning and fitness of course compared to Barcelona.
I don't see any significant difference, both Real Madrid and Barcelona will play strong teams from Bundesliga. I'm very sure Real Madrid and Barcelona will be very serious to win the matches because they are not in the safe position in UCL league standings. 3 points is important, Real Madrid and Barcelona needs full points to compete for the top 8. This UCL match will definitely take a lot of their energy before the El Clasico match. However, I believe both Real Madrid and Barcelona will still play all out in the upcoming El Clasico.
By the way, I can agree that Barcelona have a shorter rest before the El Clasico. The match will be also held in Real Madrid home. Sure, Real Madrid has an advantage in this match. But this doesn't mean Real Madrid will be easier to face Barcelona. Barcelona performed impressively so far, it should be difficult to beat them.
Also, based on the odds currently available, it is also clear that Real Madrid is the favorite team, because their current odds are Real Madrid @ 1.95 and Barcelona @ 3.50.
This is a prediction only, it won't impact much on the field. I think there are other crucial things that will have bigger roles. It is about the strategy (tactic), lineup, and how the mentality of the players during the match. But, I also believe Real Madrid has a higher chance to win the match. It is their home match and it is a big chance to shorten the point gap with Barcelona.