Jim, the main thing is to make money. That means providing an excellent product for a price that leaves plenty of room for profit. If you plan to grain these calves, make sure you factor into your price the costs for 1) grain and 2) your extra time.
While grain will put the pounds on them, it might not make the beef “enough better” to justify the increased price you will have to charge to come out ahead. I’ve eaten grass fed/finished beef all my life and I’d just as soon choose it as something from the store.
All other things being equal, there are two main factors that make one steak better than another: aging and preparation. Aging works wonders for tenderizing any beef, making decent beef good and good beef great. But even a great cut of beef won’t taste great if it’s not cooked properly. Marbling is also a factor, but that’s got as much to do with genetics and the individual animal than diet, and more to do with taste than tenderness.
Grain can increase the rate of gain, no doubt. But I think the jury is still out on exactly how much it improves the taste or tenderness. Some? Sure. Enough to be worth it? Not so sure. It’s just my opinion, but it’s based on a lifetime of dining experiences - ha.
Bear in mind that these statements are made in the context of a private individual who is direct marketing his calves. The point is that selling calves direct to the consumer is a royal pain in comparison to regular producing. The main thing is to not underestimate the amount of time it will take you, and therefore make enough money for it to be worth your trouble. The net price to your customers should already be significantly higher than the grocery store, for grass fed calves. If you factor in feeding, then getting it high enough to be worth your trouble might make it too high for your customers.