Probably or possibly, given the time frame. This is not carved in stone and at the minimum I'd recommend a thorough reheat. If you want to take a chance then think about how the food was handled after cooking: Was it actually handled--i.e., physically touched? Any errant coughs or sneezes? (Both set up a strong possibility of Staph. aureus contamination--people are the big carriers/cross contaminators when it comes to Staph.) Any chance the meat was cross contaminated in another fashion? Not sure? Pitch it.
The problem with cooked food is that spoilage bacteria were destroyed when cooking occured. Though new spoilage bacteria will start to colonize in the circumstance you note, so will pathogenic bacteria. Heat resistant toxigenic and spore-producing bacteria are especially the concern as these are often an issue in cooked-then-temp-abused foods. Since spoilage bacteria are not in abundance--as they are when the food is not yet cooked--there is little competition to delay the growth of these pathogenic bacteria. Slow cooling is a big problem--especially if the meat stayed in the rather critical range of 80-105F. Were my kitchen especially warm I wouldn't think twice about pitching it.
Time is the other critical factor. It takes time for most pathogens/toxigens to grow to sufficient numbers to cause illness. (It takes few E. coli O157 though. They are controlled by cooking but care must be taken that no cross contamination occurs post cook, and, should this be suspected, reheating is thorough) This is the 'why' behind the 4-hour rule--the time factor. Note, though, that growth of harmful bacteria to a dangerous point also concerns the quantity of bacteria that were possibly introduced: if I left a hunk of brisket on the counter for 5 or 6 hours I might reheat for breakfast--but I know exactly what the possibility is of contamination because I cooked it, dealt with it after cooking, and left it there. I would not reheat your brisket on your counter because I didn't remove it from the cooker and have no knowledge of its handling.
A 5- or 6-hour left-on-counter stretch is not likely to be sufficient time to cause illness in most cases but it is possible, depending on the meat's handling after cooking. That's the best answer I can give you.
(Remember, too, that young children, the elderly and the immune-compromised are less able to handle an illness caused by pathogenic contamination. Don't serve them questionable food.)