Another Idea if you have the time is to build urself a new parcel shelf to accomadate (sp?) the new speakers.
Its best to build it out of 20mm MDF - the advantage is that the mdf gives u a surface that is more rigid to mount the speakers into. it will make your speakers sound a thousand times better.
When i first installed my 6x9s in my corsair i installed they sounded terrible, but after building an mdf parcel shelf they sounded really good (in comparison)
The other advantage is that when u want to sell ur car, i u like u can take out the speakers and put the orginal carpet shelf back in keeping it looking nice and tidy
And in regards to the front speakers, i took the map pockets off and am in the process of building replacement ones to mount my speakers into. at the moment they are just off with the speakers in the door.
Thats my $0.02
Ps i no longer have any rear speakers and when i took them out i was extremely glad i had kept the old shelf