I'd say 2 as I don't recall any single core chips around (hehe!). Joking aside, there is only so much one can do. Take a look at the past contests and let me know how many G3258's were in the comp? I would venture a guess that it is less than the number of Intel Hex's and octo's (though, that seems counter intuitive due to the price, I may be wrong?). You are not going to be able to please everyone. What you are looking at is pleasing the vast majority with the least amount of effort while still getting a good run of the bench. I believe a 4c/t limit does this as best one can with the least amount of effort for the parties involved.There really is no safe number of cores but 1 or all. A G3258 wouldn't keep up with an i5
Anyway, I said my peace... and a lot more as usual. I will participate in just about anything assuming I have the time.