Hard in what way? The prelim surgery residents here get fairly annihilated (and this is common at many places) with several rotations averaging > 90 hours a week. 6 days per week just about the entire year. The medicine prelims here get outpatient rotations and elective time and don't spent NEAR as much time in the hospital.
Honestly I don't know many people that willingly choose to do a surgical prelim year, there typically isn't much education and scut work is pervasive (consult H&Ps, discharge summaries, receiving OSH transfers, getting people to rehab, etc...). Almost all either failed to match in GS or some other specialty. Almost all of our advanced residents complete a medicine prelim year or a transitional internship. Finally, advanced residency slots are drying up and many programs are going to mostly categorical spots - any reason why you aren't interested in that?
Anyway, back to your original question, you have solid stats and shouldn't have any trouble securing a prelim surgery spot. I'd try to do it at your home institution or your future advanced institution (there still are some residencies that don't have any categorical slots) to minimize moving over the next couple of years. I don't have specific numbers, but I would think if you could get >6-7 interview of prelims than you'd be fine.