You may find many confusing answers to your Q but I'd bluntly say NONE! The CK exam tests your clinical knowledge and the part that would relate to step 1 is "Knowledge of disease mechanism" which is a section very well covered in all CK books the rest is simply up to you in focusing on these information. For example, on my test i encountered 3 Q asking about the underlying mechanism causing hypercalcemia in 3 disease entities (multiple myeloma, sarcoisdosis, etc) and overall i did pretty well on that section of the test Best of luck
I'm in the same position, although i'm nearing the end of my revision time - my CK exam is in April.
I haven't found that I'm massively held back by not doing step one first. As others have said, it is much more about clinical knowledge and decision making.
The one thing that I'm struggling with is cardiac catheterisation and results from things like Swann-Ganz catheters i.e. intracardiac and pulmonary pressures. Apparently, these are requesite knowledge for step one and are covered in some step 1 texts, but less so in step 2.
Other than that, I think it works to take them out of order as an IMG.