I might just fletch 8 with the helical and 4 with the straight offset to see if there's any difference. Using wraps and tape makes it easy to change if one is obviously better than t'other.
The problem that you are going to have is that you won't actually see one being better than the other. What you will see, without doing actual statistical analysis, with plotting results and such is that what you want to be better, will appear to be.
Perfect results, ie, six arrows that will go into exactly the same hole at 25 metres has been achieved with offset fletching, so considering that helical is going to improve on that is a bit of logical fallacy, as is expecting that it will be worse.