hey mate, your running really light gear so just a standard EQ5 will be ample sufficient.
No German Equatorial Mount (GEM) will auto align as there is physical adjustments to be made unlike a Altitude Azimith mount (ALT AZ) that can "semi align itself" but if its photography you are looking for then go the GEM.
As for the precision that you will need in regards to wide field photography although you have to be reasonably aligned it isn't as critical also you don't need to guide at that focal length as long as your subs are around the 4-5 minute mark much over that and using something like the finder guider package that Orion offer will be very good for your setup.
https://www.bintelshop.com.au/Product.aspx?ID=9193
Things that you might want to purchase in addition to the mount;
Rotating ball head (so you can get the right framing)
Side by side setup (so you can run more than 1 camera at a time eg your 200 with your 50 this isn't essential but could be of good benifit)
An astronomy package something like "back yard EOS" or the like is very handy
With your cameras they have a daylight filter that will block most Hydrogen alpha wavelengths (red nebula) but you may still get a faint hint of these nebs at such a wide field. So in that case using the clip in filters are pointless unless you are using the light pollution blocking ones for shooting in the city (not really advisable in anycase).
As for the selection of what camera to use try to use your 1D as the full frame and superior noise control will give you really nice images one of the members of this site Hymuan (sorry if i spelt your name wrong) who frequents the terrestrial photography area has alot of experience with this type of photography with DSLR's
Hope that helps and here is a quick glance at what a Standard 40D guided at 2 min exposures stacked with the standard 18-55mm (i think its those numbers) will do.
http://brendanmitchell.net/?page_id=...oto=71&occur=1
http://brendanmitchell.net/?page_id=...oto=72&occur=1
This one is with a standard canon 55-200 i think it is zoom lense at 5 min exposures stacked
http://brendanmitchell.net/?page_id=...oto=73&occur=1