The improvement in acceleration (so called pick) and smoothness of engine sound is usually a good indicator. Although it is not technical definition of a better engine oil.
I do not drive a Toyota, however, I felt this drastic improvement when I changed my engine oil from Liqui Moly 10w-40 (Made in Germany) to Mobil 1 New Life 0w-40 (Made in France). LM is semi-synthetic and Mobil 1 is fully synthetic with cleaning agents. So technically Mobil 1 will always come out darker, since it is designed to keep cleaning the engine as it is pumps through.
I have parking in basement of my office, and when I am leaving, I have a steep rise of about 4 meters in short distance. I felt a huge push after the oil change, and the engine felt eager to take on the challenge. Similarly, the sound of engine became smoother after the oil change. This is more pronounced after a cold start.