Sheraz, here is a brief reply. I shall be back insha'Allah if I see something positive from your end. First of all, restrain from name-calling and I shall do the same.
The first point to state is: Sunnis do not hold everything listed in a Sunni author's book to be authentic or to be the "Word of God". We believe that Sunni authors can make mistakes. Hence simply stating "Sunni references" does not prove anything. Instead of this I would prefer if you could post the isnaad (line of transmission) from the books, so the isnad can be investigated to see if it actually does originate from the mentioned person.
Now as for my response to some of the questions you raised in your post:
You say that the verse refers to Mutah since the word istama'tum is used. We know that the words of the Quran must be seen in connection with others, instead of being viewed independently. So we read on and we come across:
Point #1:
4:25 - And whoever of you have not the means wherewith to WED [yankiha] free believing women ..
Hence we understand that the preceeding verse is also talking about nikah and not mutah.
The mentioned verse further goes on to talk about Mahr etc, and who to marry etc, hence further establishing the context.
Point #2:
The various forms of the root word (m-t-a) have been used in various parts of the Quran without referring to mutah. I shall look this up in detail if you want, although I feel that you are well aware that the word does not necessarily mean 'sexual relations with a female' :-P
Point #3:
"...And those who abstain from sexual intercourse except with their wives (azwajihim) or those whom their right hands possess. [23:5]"
In this manner, we understand that the original verse does not refer to mut'ah since the above mentioned verse mentions that apart from our wives, or whom our right hands posses, then everything else is unlawful.
Do the females one is conducting mutah with (err.. i dont know the right term for what that might be..) do they fall under wives or those whom our right hands posses?
The other thing that you talk about, is that Umar (ra) made it illegal. This can not be taken as true since many of the Prophet (saww)'s companions were alive at the time, and would definitely have changed the practice back if such had been the case. Infact if Umar (ra) had changed something which the Prohpet (saww) had commanded with, then I do believe that the Caliphs after Umar (ra) such as Uthman (ra) or Ali (ra) would have made it legal again. I dont believe there are any references to show this.
and 
instead of 