There is no BLE with 'proprietary protocol', you're either using BLE, or you're not using BLE. BLE is defined over an underlying 1Mbps link, however the actual throughput after you take into consideration
The overhead of the protocol
The fact the link is half-duplex
The limitations in BTLE stacks (all of them) which restrict the number of packets which can be transmitted per connection interval
The limitations of various communicating devices which may limit how often devices connect
Whether you are writing packets requiring responses or writing without response and dealing with dropped packets.
This thread does a good job of summarising what's actually even possible
