I'm getting conflicting information...
 

Does anybody know what size the door speakers are in an 06' Impreza RS and the max mounting depth the doors will allow. I can't find this info anywhere and I don't want to take the door panels off in this cold!!! Thanks.

Check out sites like Futureshop and such. They have vehicle speaker sizes. I think Pioneer has something on their site with the same info... don't quote me on that though.

I dont know if imprezas are the same, but the legacy has extremely shallow speakers in the doors because of the window rails. The only speakers that i know would fit that were the Hertz Space series components...theyre 799.99 at east hamilton radio...lol. Good luck!

The info I have says you will be able to fit a 6.5" speakers and you have about 2.5" of depth into the door to mount speakers.

http://www.mobiletoys.com/partners/infinity/pages/whatfits.aspx
Front: 6 1/2x2 1/2
Rear: 4x2

JBL's site says the same thing and has photos.

JBL Vehicle Fit Guide

If it's 2.5" deep then most 6.5" speakers will fit, particularly if you use a .25-.5" spacer/adaptor that's normally needed to install the speaker. So basically, anything up to about 2.75" is safe for a direct install (with suppied adaptor), or up to about 3" if you have thicker spacers made for them. In other words, just about all 6.5" speakers will fit.

Thanks for the info guys. Much appreciated.

Check out MR2NR's sale on the MBQ Premium 6.5" components! Great deal.