hey im a straight guy who carries a speedy 40, 35, 30 and in all different patterns and im also average height (5'11.5') and all it matters is your confidence... i would suggest to you dont carry it on the crook of your arm, handcarry it, it would look somewhat more masculine... and also with the speedy 40 make sure dont load it up to the max its gonna be really heavy and eventually you will get sick of carrying the bag... oh you need to have some sort of organization skills as the 40 is HUGE, like you will be digging through your bag just to get your keys or something so you might need to have little bags inside the 40 itself so you wont 'lose' stuff inside your bag...
you will look great with your speedy 40 as it can be dressed up or down, all it depends is your confidence and if people make fun of you or stare at you, all you have to do is hold your head up high and just ignore them... i get these stares all the time and get called gay and stuff but i dont care, its good to be different and unique so i would say go for your speedy 40 you can rock it... oh look at the clubhouse "Men Carrying Speedys" and you will get an idea of how guys here rock their speedys!
Good Luck!!!