@EllsKBells - I think I answer all your questions relating to accuracy in this post:
http://www.diabettech.com/cgm/whats...n-easy-question-with-a-more-difficult-answer/
My experiences with the G5 are that it is a lot better than the Libre in terms of closeness to BG levels, and is my preferred sensor/transmitter pair for running a closed loop system. That you can also calibrate it as part of the set-up is also good.
The G5 doesn't currently link up with any pumps, you'd have to use the G4 for that, and in the UK, the G4 doesn't come with the 505 algorithm, so has a MARD slightly worse than the Libre. The other thing about the G5 is that the Clarke Error Grid compliance is 92% zone A and 99.5% Zones A+B, which is very good.
If you go with the G5 Dexcom, and use an Android phone with the xDrip+ software, you can get about 140 days out of a transmitter, so for me, with 16 days per G5 sensor, my annualised cost with the G5 is about £1675.
With the libre, again using only an Android phone and Librelink software, you pay about £1225.
On the G4 with about 21 days of good sensor use, I annualise at around £1200 as the sensors last longer and I was able to get a G4 transmitter without a receiver and use open source builds for capturing the data. If you have to buy a Dexcom receiver, it works out at about £1400 for the G4, but if you get an Animas pump, you don't need the receiver.
Lots to think about there though, so good luck!