I am a big believer in compromise in relationships, but I think it's your husband who needs to compromise on this one. Your budget simply doesn't allow for you to go with the high-end appliances, because the rest of your kitchen will look low-end by comparison. You need the entire kitchen to look good. A Sub-Zero fridge and Viking stove aren't going to hide the fact that the cabinets need to be replaced, the floor is mess and the countertops are cheap.
The experts at Remodeling magazine estimate that, on average, 75% of the cost of a mid-range kitchen redo can be recouped. So on a $20,000 project, you'll be lucky to "get back" $15,000 or so when you sell. And you aren't going to help your cause if parts of the kitchen look dated or shoddy.
Besides, I can guarantee you that at least 99% of your husband's desire for these two items is purely about status. He's got appliance envy. It can't be solely about looks, because there are plenty of lower-cost alternatives now that have the look and feel of high-end stainless-steel appliances. And it's not about your performance, either. Yes, the Viking delivers extra firepower. But a fancier oven isn't going to turn you into Emeril Lagasse overnight. And the deluxe fridge won't make a carton of ice milk taste like Ciao Bella gelato. Top-of-the-line appliances are luxuries, not necessities—and with a $20,000 budget for your entire upgrade, you can't afford to spend 40% of your entire budget on them.