There are reported issues with using the same SSIDs and passwords although some have it work fine for them. I have not done it but I suspect it may vary by the connected devices.
I like to have separate SSID names for several reasons.
I can control which devices go to each band.
Not all devices will work on the 5 GHZ band.
Some routers will revert to the slowest connected device and use "B" or "G" instead of "N" or "AC"
Since the 2.4 band tends to have more distance than the 5 GHZ band devices will tend to connect to it especially if you are near the limits of the 5 GHZ band. If I am near the router, my iPad connects to the 5 GHZ but in the bedroom, it connects to the 2.4 GHZ. However if I connect to the 5 GHZ and then go into the bedroom, it stays on the faster 5 GHZ band.
The 5 GHZ tends to be faster than the 2.4 GHZ band so you may want certain devices to always connect to it.
Most devices such as phones and tablets will allow you to set up multiple networks and they will connect to either one much the way the same SSIDs does for you now. Printers and such allow only one network so you select the band you want the devices on.
Anytime you debug a problem, if you can isolate something, the better.
As for the performance upgrade, I think you will need to contact support directly for more info. I use email as I tend to get better answers.