I'm assuming that you're using a website speed test? All the website-based speed tests I know of are single threaded/connection type tests. You'll need to use something that can create multiple connections, like iperf to full test the PTP550 when using channel bonding. You can find out more about the PTP550's channel bonding and load balancing features HERE.
PS. in the future, please make sure you post your questions under the appropriate forum area. For this question you would have wanted to post it HERE. By posting to the correct area you will be more likely to get a response.