USDA grades like Choice and Select have subgrades. Rancher's Reserve is one of the best grades of USDA Select. Your roast is probably rolled somewhere ("rolled" means it has USDA "stamp" marks from the inspector), unless it's been trimmed off. What it comes down to is that a Rancher's Reserve top sirloin is a good cut, from the top end of a mediocre grade.
You can certainly cook the whole thing and store it cold for thin slicing and sandwiches, but top is too good a cut to use all 12 pounds of it that way. After rib, it's probably the best cut for roast beef.
Of the great steak cuts, top is not particularly tender compared to the loin and rib, but it's the most flavorful. In terms of tenderness, it may not be "particularly tender" as the others go, but it's darn tender compared to the rest of the beeve.
It's not a "po' folk" cut, and certainly does not require "low and slow," braising, or any other type of workaround cooking to bring out its best. On the contrary, those techniques are more likely to ruin it than not.
It's the traditionally preferred cut for "California Beef Barbecue," and is easier to deal with than its competitor, tri-tip. California Beef Barbecue means cuts about 2" thick -- half way between a steak and a roast; then cooking it with a mix of direct and indirect heat -- again, halfway between a steak and a roast, on a wood or charcoal fired grill. There is no higer use.
Mary's suggestion of smoking it, goes along the same lines. The one caveat -- which she implied by talking about "rare" -- is not to overcook. Top sirloin is a fairly lean cut, and, with a few exceptions, you don't want to take it past "medium" or it will get dry and tough. So, include that in your plans.
As to butchering, break it up into three or four roasts, sized as whatever qualifies as dinner plus leftovers in your family (1 lb per person allows for waste, big portions for the boys, and leftovers); break one of those roasts up into pieces small enough to make meals of sukiyaki, stroganoff, chicken fried steak, carne asada, or whatever; roast the first in your usual way; and freeze the remainder for later.
As a sort of "rule breaker," it might be worthwhile to mention that I like this cut very much for a particular sort of chili or curry. That is, I grill it as a large piece over high heat to get it black and blue, before dicing it. You can use leftover grilled steak in the same way -- or even leftover roast, but you won't get the same "char."
It also makes very good hamburger; but it's lean and you want to be very careful about overcooking. If rare hamburger is your thing, top sirloin may well be your cut. Top is also good for tartar, if you do that. Have capers and onions, will travel.
Enough bandwidth already. So, I'll wrap it up.
If "roast the first in your usual way," seems iffy, ask and I'll write a recipe for roasting a top sirloin. I should post one anyway. Ditto for "California Beef Barbecue" if your weather is up to it. As to the specifics of the other dishes I mentioned -- don't overcook; and if you need a recipe it can probably happen.
Let me know,