Hi there Bob, I would cook them like this.
Sirloin Tip Roast: Season with salt, pepper and garlic powder. Dust with flour and using a roasting pan if needed, brown all sides on top of the stove in olive oil. Only turning 1x per side. Then stick a thermometer in it and cook it at 350 degrees until 120-125 degrees at the thickest part. Remove this roast from the oven and let sit for about 10 minutes. Then slice paper thin. Serve with horseradish sauce and/or bernaise sauce. So fantastic! To me a rare slivered roast beats a braised roast any day!
For the pork loin: Season with salt, pepper, garlic powder and if you would like rosemary and thyme. Then smear liberally with countrystyle dijon mustard. Dust in flour to coat and shake off excess. Then place roast in a roasting pan and into a preheated 500 degree oven. Leave the oven on 500 for about 10 minutes. Then reduce heat to 350 and pop a thermometer into the thickest part. Cook to about 160 degrees and remove from the oven. Let the roast rest for 10 minutes then slice it thinly. The roast will still be moist and pink-ish in the middle. It will be cooked through however, and you don't really need to worry about overcooking pork with commercially produced pork these days. A bit of pink is fine and won't hurt anyone.
The meats will cook at about 20 minutes per pound assuming they aren't frozen inside. I would take them out of the fridge about an hour prior to cooking. I would rinse and dry the meat well before seasoning and when you coat with flour I'm not talking about "true breading" you are just lightly dusting so you want a film. Nothing too thick. The pork roast film will be thicker because of the mustard but it is still thinner than most breadings you may be thinking of.
I've grown up cooking roasts like this in the old southern tradition and everytime I make them, I get rave reviews. I also make pan gravies from the fond remaining on the bottom of the roasting pan. I serve the sirloin with mashed tators and pan gravy and serve the pork roast with Uncle Ben's rice and gravy. I'd serve southern veggies with them like maybe squash casserole, turnip greens, okra and tomatoes, corn bread....mmmmm mmmmm!
Plan on about 6-8oz per person as a generous serving. The women will eat less and the men more and it will average out. Especially if you are serving lots of other sides.