I own the ES7, classic Mo Rack and the S90. I'm sorry that I can't offer any tidbits about the ES Rack's arp, or the classic Rack's arp for that matter but I can say the difference between the ES rack and the classic rack was certainly not significant enough for me to get an ES rack. I got a classic rack, in a nice 2 space rack/bag for 500 used on eBay.
My only point here is before you go with an ES rack, closely compare it to the classic rack. you may find you can save some dough if you can go with the classic rack.