I've got a long (over 1/2 mile) driveway that is very steep in two places. I'm going to get some gravel here soon but am not sure if I should get 21A or 57. I'm leaning towards 21A but wanted to hear from you guys. I think the 57s would be too loose when traversing the two hills. Also, in terms of raking it w/ a landscape rake, how do you recommend? I'm guessing rake angled in to bring extra substate to the center to keep the crown high? Any help on both matters is greatly appreciated.