I really think the ultimate 60% with arrows allow for 6 keys on the bottom row aside from the arrows and space. Personally if I could get left control, left alt, left win, right control, right alt, and a function key in there somewhere (anywhere), it would be awesome. D allows for that, but with a small space, which isn't optimal. I would sacrifice and go with a non-standard arrow key layout (up arrow on the right of the right shift, move all arrows keys to far right) in order to fit extra keys on r4.