i have built many panels over the years, i have not ever added a 7th button. I personally don't play alot of fighting games, but i do play them occasionally. My boys play them frequently. I don't think i am going to bother with the 7th button, but if i did, i'd probably put it to the right side of the top row, and program them like this:
1234
456
i know that doesn't give you a thumb button for mk3, but as infrequently as i play it, i don't mind using one of the middle buttons. I naturally reach to the top row for button 1, so moving it to the bottom row feels unnatural to me. I hightly doubt i will add it..i have to look through my box of buttons to see if i even have enough blue and orange buttons to do so. thanks for the input guys.