I just did up my 4850 last night with an S1, so I have a few observations:
1) I couldn't figure out how to get AC's VRM heatsinks to fit over all the little power FET chips on the end of the card. There are 8 of them arranged in 2 squares of 4 chips each, while the included heatsinks seem more appropriate for chips that are arranged in long rows. So I used a pair of leftover ramsinks from a Zalman VF700 cooler. Each of these was just big enough to cover an entire square block of 4 FETs. I used the AC sinks to cover the 4 choke coils to the left of the FETs (this left some parts of the chokes uncovered, but I'm hoping that these don't get as hot as the FETs.
2) Regarding your thermal pad selection. I could be wrong, but I don't believe thermal pads and thermal tape are the same thing. Thermal pads don't necessarily have adhesive properties and aren't designed to hold a heatsink on by themselves. Rather, they're meant to be used in place of thermal grease (like your AS5) on a heatsink that is held on by other means (screws, clips). Some pads are tacky enough that you might think they're adhesive tape when they really aren't, so keep that in mind. I don't know anything about the specific ones you linked to though.
From what I've read about the thermal tape on the Accelero sinks, it will work okay, as long as you make sure to thoroughly clean all the chips, and also press them down firmly for at least 30 seconds (some people recommend preheating the chips with a hair dryer. I used a little heat and they seemed to stick well enough (knock on wood). For the Zalman heatsinks I replaced the Zalman tape with Chomerics Thermattach T411 (T412 would probably have been better in this application but Sidewinder Computers was out of stock).
3) Size. With a 120mm fan attached, this thing is a monster. You will need at least 3 free slots next to the card, not including the 4850 itself (so 4 slots total). Crossfire is out of the question without some creative fan mounting/ducting. Thankfully my motherboard also has a PCIe 1x slot on the other side of the graphics card slot, so I at least have one accessible PCIe slot for my eSATA controller.
Hmmmm, maybe I should pick up a pack of the Zalman heatsink coolers for the RAM, and then use the rest for the other bits.
The Asus card not only has no cooling on the rear components, but not even RAM coolers!? Actually, a lot of the cards are like this.
I guess I will just skip the thermal pads.
The 4850 is the only card I have, and despite having a P45 Gigabyte board, not really interested in doing SLI, so I should be good.