What are your goals? Is this for gaming? Is it for productivity? Are you running heavily threaded applications?
There are two big perks to the E series chips: More cores, and more PCI-E lanes. So if you're using it for work and run heavily threaded software, and get paid by the project Haswell-e will help you get more done faster. Haswell-e also has access to 28-40 pci-e lanes (dependent on which CPU you buy) vs the 16 lanes available on mainstream i5 and i7 chips. The lanes can be used to provide bandwidth to either GPUs, or to new and faster storage standards (M.2 and SATA Express). But not both at once. If you want to run more than 2 GPUs and a pci-e 4x M.2 you pretty much need the Haswell-e.
The bang for the buck CPUs have always been the i5 K series CPUs. The Newest Devil's Canyon i5-4690k will be a fantastic CPU all around. By default it turbos to 3.9GHz, but being K series it has an unlocked multiplier. It's $170ish cheaper than the low-end haswell-e i7-5820K, and will use more affordable DDR3. Personally, I don't believe DDR4 has been developed into an interesting product yet. The only real advantage is has over DDR3 is lower operating voltage. Sure, the frequencies are much higher, but so are the latencies. It balances out, and I doubt there's much performance improvement to be had in going to DDR4 for now.
The biggest upgrade for you will be having access to SATA3 (and faster if you select a Z97 motherboard). A single Sata 3 SSD will be as fast as your current RAID 0 SSDs.