On the family property we use Trimble and we have it installed in a Caterpillar Challenger 35. We are row crop farmers and need the highest level of accuracy which is RTK and that gives us <2.5cm pass to pass and year to year repeatability. We have the Trimble FmX Display in the cab and utilise the automated AutoPilot steering system.
Reason for Fmx Display was for the GLONASS receiver which means we pick up 6 Russian satellites plus the 11-12 Americans satellites giving us better satellite availablity, down the track want to use yield mapping, water and field management options. We just preferred the AutoPilot over the EZ-Steer because we didnt want to mount anything to the steering wheel.
Where I work they have 6x JD 8320, 2x JD 7930 & 2x JD8520T all kitted out with JD GreenStar StarFire iTC RTK. In the past 3yrs of working with the GreenStar I have never seen it maintain <3cm accuracy across the whole farm. It doesnt matter if your 200 metres or 4.5km away from the base station. We have had JD out calibrate recalibrate still no result. I remember one day a 7930 pulling a 5000Ltr 24mtr boomspray saying 3 -5cm then coming back to the same field 2days later for water test run and it was saying it was 30-35cm out on the same AB Lines - I shake my head. Another day pulling up 12Rows with a 8520T the GPS would fall out for it to reconnect I would have to drive around the farm and then try to get back to where I was plowing while trying to hold connection sometimes it would take 30mins to an 1hr for reconnection and thats with 11 or 12 RTK correctional satellites. And as soon as you fell out to 9 RTK satellites you then dont have RTK accuracy and start falling down to the next level of accuracy.
With the Trimble in the 2.5yrs of having it dad has lost all GPS correction for no more than 10sec. It happened while turning to enter the next AB line he than stopped, reconnected within 3sec, backed out and re-enter the field and thats it. It will even work while the tractor is in the shed.
When we were looking into GPS we looked at Trimble RTK & John Deere StarFire iTC RTK with GS2 2600. Trimble was less than $3000 cheaper, Service call outs were cheaper with Trimble, Trimble has a far longer range from base station to tractor reciever, more optional features, better terrain compensation with less moving parts. But for me the biggest comparison is just look at what JD has done with GPS and now compare that with what Trimble does and thats why when it comes to GPS technology theres only one place to look at - Trimble
For harvesting in my eyes I would be wanting the best pass to pass repeatability so that the header front was being utilised to its full potential but I dont know what your bottom line is but maybe in your case I wouldnt be going for less than 5-10cm pass to pass repeatability. I couldnt answer if there is or how much of a cost is involved for this level of accuracy, my guess would be yes there is.
For Trimble GPS speak to the guys at BMS LaserSat these guys are the direct importers for Trimble in Australia and they will surely help you out and answer any of your questions.
BMS LaserSat Moree
429 Frome St, Moree, NSW
Ph: (02) 6752 4647
Fax: (02) 6752 2470
Website: BMS LaserSat
Trimble Agriculture on YouTube