I've done the math on my local lotteries and the EV tips into the players favour when the jackpot gets a bit bigger than 30 million, even if you share a jackpot with one other. This is due to the return of 3,4,5,6 and 7 numbers all adding up, combined with the fact that the jackpot is largely from what others have spent in previous weeks.

If I was completely rational I'd bet my house on it when it tips into my favour. I am not completely rational.