Yes, no, maybe! The correct answer would be to save fruit only which exhibits the standard for that variety. Just because a certain plant has some fruit which are 50% bigger than standard does not mean that those fruit are genetically the same. The rule of thumb for origin of each tomato variety is that 95% are fixed hybrids. The other 5% are mutants or somatic changes. Some early-maturing varieties were produced by collecting seed only from the earliest fruit. Others were established by going through a field and picking out the largest fruit. (Many of Livingston's varieties came about that way.) There's a big fuss in the tomato world right now as to the correct Box Car Willie. Seems that what many companies are offering has larger fruit than according to descriptions in a certain book. Apparently it's identical otherwise except for the fruit size. Somatic changes can be where there are two obviously different fruit on a single plant such as yellow and red. It can also happen with fruit of the same color and that would not be so obvious. Personally, if the plant and fruit are according to the standards except for some extra large fruit, I look at the larger one as just being more seed than a smaller one!
Martin