How to set timeout using AT commands and ELM327
Read the datasheet for the ELM327 to understand the maximum message rate that can be accommodated. There is no buffer (it has only the RX and single message buffer in the chip) in the ELM327, so any buffering is done by whatever MCU they used to manage configuration and BL.

You clearly (from page 12 and page 74 on) should not turn on LF or AL if you want to get the maximum throughput message rate with least buffer utilization. 

One has to say, if you really want to investigate the CAN-bus (all messages at high speed) and are not simply trying to do OBD-II codes, you should get a serious CAN-bus analyzer such as the Microchip one.