Mirek,
I don't own two 32's. But I pretty much have one of every size KB from 8kg to 48kg. Yes I ultimately do 5x(1,2,3,4,5) for Grinds. It is a lot of reps and I probably don't need that many, but I am just following the program (I find that I sometimes have recovery issues and get stronger with less volume and more rest, not with ROTK but in general). Sometimes I do less reps when I move up to a new bell. My last workout I used a 36 and a 28. Next week ill use a 36 and 32. I don't push myself too hard with intensity or density (i am not at my limit). My workouts have been 45 min (light days) to 90 min (heavy days). They average well over 1 hour. I am not pushing too hard on the time because I am saving myself for power lifting training in a couple months. Also I don't push too hard because I have a flexion intolerant back, if my form breaks down, I'm in trouble and potentially a lot of pain. Also, I am inherently lazy!!!
On these Grind ladders, my main limitation is the double snatch. For the first rep, the program calls for a double snatch prior to pressing, just one rep. I both love and hate this rep. My double snatching skills with medium to heavy kb's aren't that pretty. Most of the time I can power them up without adding a dip to catch the bells, but sometimes my form breaks down and I have to dip down to catch them. I am getting better at these. I find these snatches light up my posterior chain. These have been the main reason I don't increase bell size faster.
ROTK really works. For me, nothing else compares to swinging, cleaning, snatching, and pressing double kettlebells. My long term goal over the next few years is that once a year I do a doubles kb program like ROTK or ETK+, in between power lifting meets, and somewhat comfortably be able to use a 44 and 48 bell.