Your Attenuation, Please!

So, in an attempt to better understand my brewing process and to help me formulate recipes, I've gone through and calculated the attenuation rates for my first five brews. The results are interesting:

Beer	Yeast	Mash Temp	OG	FG	Attenuation
Blackacre Butte #1	1318 London Ale III	152°*	1.030**	1.006**	80%
Blackacre Butte #2	1318 London Ale III	152°	1.050**	1.008**	84%
Seven-Eleven Porter	1028 London Ale	156°	1.046**	1.010**	78%
Foam Dome Stout	1084 Irish Ale	154°	1.051	1.009	82%
Mulligan ESB	1968 London ESB	148°	1.056	1.012	79%

* This was hardly a "mash" in the traditional sense, really more of a long steep.
** These hydrometer readings do not account for temperature, so they may be off one or two points.

So, 152° appears to be the butter zone for creating fermentable sugars. I'll have to keep this in mind.