A couple things.
First, ground meat is for utilizing the scraps that aren't cookable by other means. It can come from the neck or shank or belly or any other part. Usually, the worst cuts have the best flavor, such as neck, shank and plate. A fine porterhouse steak makes lousy burger. That being said, a good mix of fat to lean in the proper proportions is what counts. Second, aside from the mix, the other main ingredient is the lack of bacteria.
Store or home ground meats have a shelf life of 24 hours. Use it, freeze it or lose it after that. However, how is it possible that the plastic tubes of ground meats common in all meatcases (1 lb, 3 lb, and 5 lb'ers) show a shelf life of several weeks (actual is 45 days from date of packaging)? C'mon... its gotta be inferior tampered-with bottom crud one foot shy of getting tossed in the dumpster garbage, right? That's why it's cheaper, huh?!!
Not so... not at all. I've been to Moyer Packing Plant in Pa. (now part of ConAgra) and first-hand witnessed the beef process from live animal to ground burger and every step, every cut, every process and program there. You will walk away with a totally different view of the meat process.
Sanitation controls every step of the process, starting with dress code. Upon entering the plant you have to dress completely in hospital-style pants, tops, shoes, socks, hats, gloves, booties, masks, etc. The air is scrupulously clean and filtered. Every step of every process is monitored, and testing is done constantly. Steers heads are plucked for nose and ear hairs for fine brushes, hooves are dissected and ground for medicine, every pat is trimmed and evaluated. Primal and sub-primal cuts are produced and methodically trimmed to specification, COV'd, boxed and loaded on trucks within hours of kill. Body heat from fresh kill is dissipated by meandering through a nitrogen cooler and in 20 minutes chilled to 37° internal temp. Every 3 hours all processes stop and all surfaces are cleaned, sanitized and dried for the next startup. All trim is moved through the plant on conveyor belts and cut and put through fat analyzers to the proper fat-lean ratios, then ground and packaged in gigantic grinders, one spilling into another for a double-grind (I'm talking about grinding machines the size of tool sheds!), muscled through giant tube stuffers into whatever sizes that need to be produced, packed into cases, quick hard-chilled in a nitrogen cooler and loaded on trucks to distribution centers again within hours of fresh kill. A sanitation rate of 99.64% or better is routinely achieved. When the burger is stamped with a 45 day shelf life it deserves it; the quality and controls are that good, believe me! You will not taste better ground meats than what you buy in the tubes.
The second part is mixing beef with pork. Make sure you cook it to 160° internal to kill any pathogens. When grinding, you open up a whole gamut of surface areas you're exposing to contamination. Thinking a beef/pork hamburg is done at 130° and you will probably be seeing an ER in your near future.