Windows 7 - Last build of Windows to use a beta key..?

Hi

I have my three copies of Windows 7 PM on order for delivery when released (E version) but my build 7201 is collapsing due to various factors and I need to do a reinstall.

Would I be right in thinking that I could use the 16385 build and then use the rearm function to extend its use until W 7 is released.?
I would doubt that I would be able to use my license keys when I do get my copies as I have ordered the E full version of HP and, I assume, the 16385 build represents an "Ultimate" build.?

Or which is the last build (x64) that you ca use the beta keys to activate..?

Thanks for any help.

I believe that 7232 was the last build to use beta keys

PS 16385 can't be activated yet due to not being available Officially yet) but you can use the re-arm command to extend its life to 120 days. 16385 is Windows 7 with SKU selection...and your "E" key won't work on it

Thanks for your prompt reply
I thought that my key would not work on the 16385 build and I appreciate the confirmation. So 7232 is the last build of x64 where you can use the beta keys, might have to look around