Gears & Axles - 12 bolt with spool weight?

I'm not ready for a 12 bolt yet, but when I am if I go with a spool what is the weight compared to with a posi? I'd like a rear end that is the same weight as my current 10 bolt. <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" />

Figure my Strange 12 bolt added about 36lbs to my car. It's a big axle Eaton posi version with ABS only.

So a spool probably saves 15# off that?