In the absence of original writing, a believer needs to choose only one Greek text of NT to follow as equivalent to the original writing. For this, I look into the context of the subjects dealt. For instance, in this case of Roman 8, if we closely read verses 4 to 9, 12 and 13 and understand what has been said, we can realize how the KJV version of Roman 8:1 is worth in its full form. This KJV is the derivative of Traditional Text of Greek NT and it is my strong conviction that Traditional Text is in line with the original writing. The second part of the verse 1 in KJV cannot be just an additional emphasis as you mentioned, because no one has the authority to add their own words to ‘support’ God’s words. God’s words are self supportive. For me, the second part of the verse in KJV is not an additional (added) emphasis, but an integral part of the verse.
As read in the ‘gotquestions.org’, it was in 1881, Brooke Foss Westcott and Fenton J. A. Hort, the two persons printed the first Critical Text dismissing the Traditional Text as an inferior one. ‘gotquestions.org’ supports Critical Text, but I do not. It is said that most of the modern time translations are made based on the Critical Text and this Critical Text itself underwent several revisions.
Please go through Roman 8:10 as given below and find out whether the two versions share the same meaning or give different meanings.
And if Christ be in you, the body is dead because of sin; but the Spirit is life because of righteousness – Roman 8:10 (KJV)
But if Christ is in you, then even though your body is subject to death because of sin, the Spirit gives life because of righteousness – Roman 8:10 (NIV)