The 35mm is out because you already stated that it does not yield the results you want.
The medium format camera does.
Learn to be faster with the 500c and because it bigger, it will be harder for someone to take from you without knowing! LOL
Or, a third option is to rent something that gives the speed you want along with the image quality that's insured! Um, digital would be about right... so you don't have to carry all that film around. LOL
A compromise would be to borrow or rent a digital back for you MF camera.... just saying.