Hickory and apple are both a sweeter smoke...somewhat sharper with hickory, but should not be an overwhelming flavor on beef. If there was not a bitter flavor and/or numbing/tingling of the lips or tongue, then your smoke chamber ventilation would be adequate...if bitter taste or tingling/numbness, you need more ventilation (creosote is forming on your food from stagnant smoke). A very strong flavor can occur if your smoke was thick and white for extended periods with the meat in the smoke chamber. Some white smoke when wood is added is normal, and nothing to be concerned about...it should turn from white to thin blue eventually, and at times be translucent (so thin you can't even see it, but can still smell it coming out of the vent). At higher chamber temps the meat isn't smoked as long due to taking less time to cook, so there would be less opportunity for smoke accumulation on the meat, translating to less smoke flavor.
A heavy dose of the rub may push the taste buds a bit. Higher chamber temps can sometimes change the overall flavor profile of rubs, depending on the ingredients...makes them a bit more intense at times, bringing out more flavors of the spices by releasing their oils. Sugars in rubs don't generally stand up to higher heat or low & slow on really long smokes, as sugars can caramelize (browned), then scorch (nearly or completely blackened)...this can cause quite a bite to the flavor of the bark on the meat.
I'm just shooting in the dark here...does any of this seem to hit on what you experienced and what the conditions were during cooking? Come on back and we'll figure this out...just need more info to identify the likely cause(s).
Eric