I am still on r83. It have been very solid for me. Welp a few days ago my GPS just stopped working and errors out even ever I try to turn it on.
Once I have something working, I tend to leave it alone. As such I am a bit out of the loop on the newer rom versions.
What is/was MK4 ?
They are our Sprint Version lettering used for at the end of the numeric sequence of the Baseband, Rom, Build Number, Software version.
MC2 is 4.1.2 Jelly Bean
MK4 is 4.3 Jelly Bean.
MC2 R105 is the most stable one to date, well was for me. 4dot3 R3 ( brought you to MK4 ) is good as well but many had some trouble & complaints. That one was not fully completed but I liked it to where it was though. Your choice on where you want to go on this one.