Corn head maintenance is pretty much correlated to acres per row.  If you run more rows, you will do more acres between row unit rebuilds. 

I think higher speeds do increase the importance of matching rows.  

Over the years, we have fit the planter to what we wanted for the combine.  We went to 8 row when we would rather have had 12 so that we could run 8 row heads.  Then 16 was pretty much what we wanted on both counts.  Then we went to 24 so that we could go to 12 on the combine.  Funny how 12 on the combine "would never work around here" when we looked at 12 row planters, but we're still 'around here' and now we changed planters to allow 12 row combines.  I've seen a lot of those type of deals in our 40 years of history.