The killer of Wifi is interference. Interference causes network packets to be missed, which causes resends, which clobbers throughput.
Wifi uses radio frequencies that are also used by cordless house phones, things like alarm systems, and home automation. Microwave ovens also leak these frequencies when they are running.
And of course another Wifi operating nearby also may be using these frequencies. Perhaps from a neighbor's Wifi. Putting you own Wifi transmitters close together may also cause problems.
Connection Strength is not a measure of whether interference is present or not.
However, the higher you can get the Connection Strength, the less likely you'll be impacted by interference. The key purpose of the extender OPPO provides is to allow you to reposition the Wifi dongle to increase Connection Strength. Try to get that to at least 70. The higher, the better.
Wifi systems operate on a range of "channels". Typically your base station will pick a channel automatically -- when it is turned on -- which it thinks has the least interference. The problems with that are (1) the channel does not change if other nearby Wifi setups turn on afterwards, and (2) the interference check happens where the base station is located -- not where a client device like the OPPO is located.
If you are in an environment like an apartment building with lots of neighboring Wifi setups, you can often get better througput by picking the channel yourself. This is a configuration setting in the Wifi base station. All the client devices (like the OPPO) will automatically adjust to whichever channel the base is using. You can see the channel in use in the OPPO in Setup > Network Setup > Connection Info.
(There are apps you can use to find out what channels are in use by neighbor Wifis if you want to get fancy.)
Generally speaking, the higher channel numbers are less likely to have been picked automatically.
NOTE: The OPPO Wifi operates on the 2.4GHz band, so it is the channel choices there (typically 1 through 11) which work. Higher channel choices for the 5GHz band (40 through 153) don't apply -- if you happen to have a dual-band Wifi base station.
Changing channels can also be a big help if you are getting interference from a cordless phone setup or microwave oven.
If you set up a VUDU account (free until you actually buy or rent content) you can use the Network Speed Test in the VUDU app (My VUDU > Settings & info) to see real throughput. This includes the speed actually achieved by your Wifi (given whatever interference is present), the speed of your Internet service, congestion on the Internet, and congestion into the VUDU servers.
A high number is good, but also see if it bounces around a lot. Random drops down to low speeds may very well mean interference is clobbering your Wifi connection.