I agree, head shape is really key, round head is more Charles Owen, narrow is more GPA and Samsheild, I sometime show in my Charles Owen but I loveeee my GPA, never changed my brand of helmet for almost 3 years now!
it really all comes down to your head shape. i was planning on getting a charles owen, but since i have a more oval head, i had to purchase a samshield. i'm glad i did, i absolutely loveeee my samshield, but you can't go wrong w a charles owen. both are great, i used to have a charles owen jr8 and loved it, besides the fact that it didn't have ventilation. if youre choosing between the two, choose between any variation of samshield (theyre al great) or the charles owen ayr8 or gr8. good luck!