If you've got the money to winter them and their in good shape then I'd winter them. Six cows shouldn't add up that much and as high as calves are they should surpass any normal winter expenses. By spring they'd be ready to wean and you could then sell your cows as bred cows and keep the calves untill the grass runs out and then sell them. I usually dont go against the grain but I always hate to sell short. If i've got a calf out of a cow then its going to at least 500lbs. before selling, she's only going to give you one a year. If I'm getting rid of a cow then she's going to be bred when I sell her as I hate to take slaughter prices. Granted there are always exceptions such as cashflow, pasture conditions and health issues but this is a very slow return business and one needs to get as much possible when it comes to selling. Best of luck!