I also think you should go with the AX-7. You can take a look at what Overclockers.com got temperaturewise for virtually all heatsinks worth concidering. The AX-7 has the best temperature to wattage radio of them all, INCLUDING the mighty Swiftech MC-462A.
I've got the AX-7 with the big Delta fan, and it almost blew me away. I had to change the speed of it, too loud. I did that and added a 120mm fan with adjusted speed, and combined they are lower than the Delta at full speed, with no temp change. As for which hsf, AX-7. It's great with a strong fan if you can take the noise. Huh, did you say something?
I don't own an AX7, but from what I've read, either one will be a great choice. I think that the Delta fan would be the way to go with either heatsink though, because it is a focused flow fan and should put up more static air pressure than the Mechatronics fan. You can try either fan on either of those heasinks though because they are both 80 mm fans. Also, from the posts I've read so far on the AX7, you will probably want to lap the machining marks off the base of the heatsink so that you will have maximum contact with the core. The posts I've read so far on the AX7 say that there is obvious machining marks left on the base the way they are shipping them out presently and this will affect it's cooling capability. I found the same problem with my 8045 and lapped it down smooth.
Since AMD is doing away with the bolt holes around the socket, I would get an AX-7 even if it weren't the best option for performance because it would be able to be used on future boards. I love the 4 bolt mounting method - it's the best by far - but 6 tabbed mounting is pretty good.
For a fan use the FFB0812HHE Delta. It's the quietest of the focused flow fans; quieter than the 50CFM Sunon even, but it still pushes 45CFM. I went from the 68CFM Delta to this one on my MCX462 and noticed no performance drop whatsoever. It's VERY quiet too.
OK guys, when you read the heatsink ratings, DO IT INTELLIGENTLY....
You can't compare the Alpha's performance directly to that of the Thermalright. THEY USE DIFFERENT FANS. In this case, the alpha had a measly (and quiet) 37cfm fan, guys, this is barely any better than 80mm case fans, and it STILL manages to cool incredibly well. The AX7 uses a Delta screamer for it's results. Now if someone were to compare them both at the same airflow, using the ondie temp reader, then you can say which one performs better...