Ordered an A6 from ZH with useful info/pictures from this site:
http://asicminer-shop.de/Avalon-6-35-TH-s (they posted before blockc)
1) Financial: There was about a net +$230 in favor of the A6 vs the S7. Part of the $230 pays for a new RPi setup from Spark Fun.
2) Engineering: From the pictures on the .de website, the thermal engineering looks better, one fan instead of two. The cooling fins are mechanically constrained to the hash board as opposed to using a thermally conductive glue bond. I think the glued fin approach in the S7 most likely forces the use of two fans at working at higher speeds. This is because of the worse thermal transfer characteristics of the glue bond versus a purely thermal conductive paste. The glued fin approach is a reliability concern.
The websites claim 80 chips for the A6, but from the pictures it looks like 9 chips x 8 rows = 72. 72 chips is also consistent with the hash rate, 3,500/72 = 50 Gh/s. Less chips means a lower supporting component count. This means higher reliability.
The other nice touch is the huge power supply bypass capacitor for each chip, mounted as close to the chip as possible.
What the engineering points to is the effort to engineer a good product without cutting corners.
