Since I updated my laptop with the Dell Command|Update utility (2014.11.16) do not have any sleep/connection problem with my 7260 wifi card. Maybe I'm a lucky guy, maybe something fixed in one of the following package what was updated:
E7240 System BIOS: A11
I2xx/825xx Ethernet Network Driver: 19.2.0.0
Intel 8 Series Chipset Device Software Driver: 9.4.0.10.27
Dell Wireless 5809/5808 WWAN Mobile Broadband Application: 6.0.4.173.8204
I use 17.1.0.19 intel wifi driver WITH PROSet! And it do not changed with the update.
I hope to be able to help with this post