The STC for both the G5's and E5 do not cover vacuum system removal in their STC. But, both units provide guidance on what steam gauges a required for backup to retain IFR capabilities (Altimeter, VSI, Turn and bank, airpseed) and if none of those is dependent on the Vacuum system it gives you a path to minor alteration to remove that system.
So, as someone that has installed G5's and E5's and has flow behind both, here is how I break down the Pro's VS Cons
G5's
Pros
-Redundancy of two screens, this is probably the biggest pro
-If installing a GFC500 autopilot they are needed and do a GREAT job of flying the airplane and the whole Can bus system really makes the autopilot install easier and cleaner as the servos are part of a "network" with the GAD, G5's, GMU11, etc... that does a great job of finding all it's components automatically.
-Garmin supports it's own equipment very nicely and if you already have a full stack of Garmin gear you know it will play nice.
-Reliability reports so far are very good, although I saw my first G5 on Friday that had a intermittent failure and would not boot up, but pulling the unit out, pulling the battery and letting it reset got it to boot up and work properly again. Will be keeping an eye on that.
Cons
-Garmin really protects it's own equipment and really pushes you to go with a full set of their gear. So, future support of the TruTrak with a G5 is in question and what is there now is very limited
-the screen size is smaller, the resolution looks poor, visibility issues in sunlight, etc... (biggest con in my opinion) Display seems "cluttered" at times with all the info you want on such small real estate
-the magnetometer is MUCH more sensitive to install location, you often chase multiple locations around until you find a clean install location.
-Due to magnetometer install mentioned above, plus the need for the GAD unit even if you aren't using it to guide an older autopilot the install times are longer by 5 to 10 hours
Aspen E5
Pros
-Screen size and resolution and layout of all the information is very good, without the divide in the information (all on one screen instead of two screens with bezel edges between them) I find it easier to scan and fly behind.
-Upgrade paths if you want to spend the money to an AMAZING display with traffic, syn vision, etc....
-Install times are not as long and I like the RSM over the GMU11 with the garmin for Magnetometer functions. The GMU11 has the look and feel of a chineese toy and considering they are going out in wings and other places where they are exposed to the environment I do wonder a little bit about longevity, but have not seen anything thus far to support that opinion, it just seems like a device that should only be mounted inside.
-The OAT sensor is built into the RSM and already wired in, you just need to unlock it. The Garmin update for OAT requires a probe placement and another module be wired in adding to install times
-Ability to interface with Non Garmin products and willingness to work with those companies more. They are working with trutrak (BK) for additional autopilot interoperability, Lynx support if you add traffic to the display, etc...
Cons
-One screen= one failure point I believe you are still much safer than you were when you had Vacuum Gyro equipment as your primary and your go to if the E5 fails is the same as where you were if the Vacuum pump were to fail (fly the Turn and Bank, Altimeter and airspeed).
-Aspen history of odd failures and reliability doesn't give the warm and fuzzy feeling.
-If you have, or are considering a GFC500 autopilot it is a no go, unless you want to add a single G5 as well to run the GFC500
My take. The E5 is a more enjoyable item to fly behind, has better interaction with equipment other than Garmin, is quicker to install, and is was my choice in my airplane having installed both and flown behind both. The biggest detriment to the E5 decision is the history of failures on past products and the single screen lack of an extra layer of redundancy. I fly behind an IFD550 with built in 3D Syn Vision via a certified AHRS, so in the case of a screen failure on an E5, I hit the 3D button on the IFD550 and I'm good to go. But, that is not an option for everyone. Other good feel good backup possibilities are to install an Aerovonics AV20 on the cheap (probably with the money you saved on the install time difference) and if you are flying with a Stratus/Stratux, etc... you have a backup on your phone/tablet with the AHRS and guidance of that uncertified unit.