What other things are you going to do with the monitor?  If you are staying away from any steering GPS, go with a 20/20.  No modules, no unlocks, no added expense.  It will do any and everything records wise.  You can then also download the free fieldview app and have the info in an I-pad.  I took my I-pad in the combine last fall and I always knew what hybrid I was harvesting.  If you want steering too, then the answer is way more complicated.  We need alot more info. 

I added hydraulic drive this past winter.  I mounted the drive in such a way that I can have my friction wheel running mechanically in about 15 minutes.