A Ranga is 38" inches. The term man-high is actually never applied in the writing to the Uruk Hai of Isengard AFAIK. They are described as Large. The term man high itself is a term relative to the Dunedain.(UT) Most men of middle Earth therefore being shorter than Dunedain would be termed nearly man high. The men of Thengal's house are specifically stated to be taller than most Rohirrim, the given reason, their foremother is Morwen of Lossarnach who actually hails from the area of Dol Amroth, an area noted for its Numenorean and slightly Elvish heritage.
The only time an Orc is specifically stated as nearly man-high is the orc-chief of Moria that stabs Frodo. This Orc is also the only orc that receives the adjective "huge", as well as some unique other descriptors.
Youll notice that in that chapter it is stated that "black uruks of mordor" are there, means this is likely to be a black ururk
Uruk Hai probably stood the height of ordinary or even smallish men given their use of mannish bows and though thicker and stronger than an average man, were not the height of Dunedain. Rohirrim infantry were on equal terms with them unless the Uruk Hai had an advantage in numbers. This I think is the point of the Uruk Hai of Isengard. This is a group of Orcs who exist in fair numbers, like too man and equal to man, in battle. Only the axe-wielding Orc-Men of Saruman described at the Battle of the Fords of Isen (UT) are likely to be man-high as the appellation huge is applied to them as well.
The Orcs of Mordor (Grishnakh), are wierd, twisted inherently more corrupt, they have a uniquely apelike quality about them. Mordor Uruks, are likely the basis of Tolkien's beast theory, in which the odd behavior at the black gate is manifested. Free standing orcs of the MM may run from battle but they do not slay themselves or gibber witlessly at the death of their Lord, they run to live then they avenge.The Uruk-Hai is a term only ever used to describe isengard Uruk-hai. Mordor Uruks are always descriped as Black uruks of mordor or simply uruks.I believe that this subject is argue between those who like Isengard more and that's why believe that their uruks are superior and those who like Mordor more and they believe all uruks are somewhat equal.
So, let's just forget what we like and bring in clear facts from books.
It's certain that they are both called Uruk-hai so I think they are more or less equal. If there is anywhere stated in books that Isengard uruk-hai were superior in training, equipment and/or strength compared to Mordor uruk-hai in training, equipment and/or strength or there are hints that Mordor uruk-hai has poor equipment, training and/or are weaker then please quote it here and at least I might change my mind in this.
if you find a quote that disagrees share