1) The technically hardest thing in the Pathetique 1st movt is the left hand tremolo. If you don't find tremolos difficult, maybe you'll be fine.2) Every person's technique is different. Some people find the tremolo in the Pathetique hard. Some people find the two-note groupings in the Tempest hard. The second movement of the tempest (especially the left hand where it crosses over) is also pretty difficult. All in all, the technical and musical challenges of the Tempest are more varied than those in the Pathetique, so it's harder.3) It's difficult to judge your ability without a video, or at least an audio recording. Have you studied Opus 49, #'s 1 and 2, and/or Opus 79? If those are all easy for you, go ahead and try out the Pathetique for size.
The people who set exam syllabuses certainly disagree with you. The pianosyllabus.com website has Op 31 No 2 (Tempest) at grade 10 or 11, while the first movement alone is grade 9. Op 27 No 2 (Moonlight) is grade 7 (1st movement) and grade 8 (2nd and 3rd mvts). Fur Elise is grade 5. There's no listing for the first mvt of Op 13 (Pathetique) although the whole piece goes at grade 9 or 10, while the third mvt alone is grade 7 or 8.