First of all, you shouldn't need to memorize over 20-30% of Chem SL. The time spent on memorizing in Chem SL would need to be spent on conceptual understanding in Physics SL. There is a clear timeline to memorization, but it is unclear how well you will fare if you have to understand a concept thoroughly. There is also a significant amount of conceptual understanding in Chemistry, in most of the units.
I wouldn't know how much the jump between grade 10 and 11 is, since that depends on your school. I took Chemistry HL and Physics SL, and frankly I do like how the physics SL course is structured compared to chemistry. The Physics SL boundary for May is around 75 rather than 80, so the difference is big but not overwhelmingly big. But physics has slightly more critical thinking questions, where Chemistry questions are in general very straightforward.
The chance that you will score higher in physics cannot be determined from the first month of IB. You should go with whichever one is more interesting to you, so that when the class does get tough, you will have the motivation to pull through. I can tell you in 2 years of Physics SL, we spent maybe 1 or 2 classes building circuit, so don't let that be a big factor. Also consider the historical performances at your school. That is more relevant than the grade boundary. If one subject clearly outperforms the other at your school, then choose that one.