I had a similar model purchased in 1996, but it was a G885SC. Similar baskets except the racks were adjustable with the middle raising, lowering and tilting. It had normal 130F and normal 150F as well as intensive and pots and pans at 170F, and some other special ones. I never had to worry about things getting clean even at 130F but the dishes sometimes did not dry as well as 150F.
The center arms washes the middle rack, but there are holes and slits in it near the end that let the water spray down over the bottom rack. The slits spray outward so when the arm turns the water sprays out across, front, back, sides, of the bottom rack. I think this might be to get the items from the front and back as the arms turn. It could complete a cycle at 150F in 70 minutes which is the one I usually used.
I bought my current DW in May 2006 but it has the same wash arm set up in the center that sprays out. This one uses alternating arms, but the center arm still has that ability to spray down out over the bottom rack. It averages 105 minutes with normal soil but it sets it own temperature so I don't know what its using.