I was growing Island gold, Fwang Tung, Kari, and Lara at the same time.
I only have Lara and Fwang left now and Lara is about to go
Most people who try the fruits prefer the Fwang tung.
I'm not that great at discerning the flavors of starfruit but I do find Fwang tung to have the least "starfruit" type flavor.
Your description of grape seems to work though, but a mild grape.
I don't find it much sweeter than the other starfruits but it's pretty good at most stages. (Don't have to wait for complete color like the rest of the yellow ones)
The two things I like about it most is the texture (some starfruits get to soft what you leave it to ripen to long on the tree) and the ridge part of the fruit is edible (sweetest part).
Also big fruits.
If your in the area and want to try some I should have more fruits in Dec