I recently upgraded from 20/5 to 50/25 and like many reporting here found the 50/25 to be lacking from wireless units. My only wired unit, a laptop, is wired only when I need to run tests. My wired speeds were roughly 60/30, my wireless speeds were roughly 25/25 on some units - other units were under 20/20.
A call to support indicated that this was all the wireless speed I could expect. They of course blamed nearby cordless phones, competing wifi signals and other apparatus.
To make a long story short, I stumbled upon this - http://www.dslreports.com/faq/12506
I bought a Netgear WNDR3700 and followed the instructions in 12506 and off I went. All wireless devices are in the 50/30 area now.
Adding this router to the MI424 enabled me to get the wireless speeds I pay for and maintain all the functions that 424 provides such a MOCA and so forth.
It is very disappointing that Verizon advertises 50/25 showing in their advertising smart phones, tablets and other wireless gear when there is no way you can get those speeds without a different router.