Ok, I use a german x51v (with a01 ROm, Dell hates german customers) and all I really need on my Today Screen are Appointments for the next few days. I tried several "Big" Applications like Pocket Breeze or some of the SBP software. I felt that all of them slow down my device. So I finally installed Calendar+ which works fine.

But now I feel, that maybe there is something that slows down my x51v less then Calendar+. Remember: I only need Appointments.

Any recommendations?

Nope - you have tried everything I can think of...