The 640 seems like without the CGM portion to be the same as any other pump. So the CGM would be critical. From what i can find out its the same system that the Veo uses (the Enlite sensors)...
If the price and accuracy of the CGM components have not changed then i wouldn't want the 640, just because the CGM is more expensive due to the shorter life of the sensors (1 Dexcom sensor can last you the span of 3 Enlight sensors) So if you add up all consumables for both systems over the 4 or 5 years you would be using the pumps they end up being about the same, but then the edge would go back to the Dexcoms Accuracy.
The 640G LOOKS way cooler then the Vibe, but its only as good as the CGM, which right now is not that great from things i have read... I hate to say it but Medtronic is putting a lot of effort of integrating their CGM when they should be putting that effort into first making the CGM better.
EDIT - The Vibe also runs temp basal rates, I am unsure of how the alarms work, but i think its good to know that your Temp basal has turned off.
You would want to use the temp basal rate for things like going to the gym, or being really active, or even going out to have some drinks. Situations when your activity level / insulin requirements unexpectedly change. Like you planned on staying home all night, and then a friend calls up and wants to take a spin class, or go for a bike ride. Its to sudden and short to use a programed mode, so you just knock down your basal rate by like 20-30% for the duration of the event and you are good to go! No more having to eat to keep your sugars up! So if you set it for like 2 hours, and the bike ride goes longer, youd want to know your temp basal rate has ended via alert so you can add on another hour or so.