Are you talking about a 6620 Titan II or a older 6620? The cab in the 6620 will be nicer. Plus you get a folding auger and don't have to worry about it sticking out all the time. As far as thrashing, I'd say the 7700 will win easily.
You can get a folding auger on a 7700 if it's a LATE 7700 just before the 7720's. We have a customer who just bought a '78 7700 that was built right before the 7720's went into production. He said it's a power folding auger.
Let me give a little more info. I am trying to compare these two machines...
'80 6620 with 2400 hours w/20 ft head with bat reel
'78 7700 with 4200 hours w/24 ft head with finger pick up reel.
(with power auger)
Both are "corn soybean models". Both are very straight and clean and seem to be well taken care of. Both shed kept.
One is $4,000 the other is $10,000, see if you guess which is which, ha ha.
Here is the thing, cost and productivity obviously point to the 7700 but I would like the better cab of the 6620 because I don't do so well with dust but I guess I could always wear a mask.
The other thing is that in my area when I am finished with the 7700 it will probably only have value as scrap or salvage. The 6620 would probably still have actual harvesting value when I am finshed with it.
Alex is correct. The 1978 66/7700's did have a hydraulic fold/unfold unload auger that was completely operable from inside the cab. This was accomplished by interlocking a couple microswithes and solenoid valves. The basic auger was still the same as all previous 66/7700's. Folding the auger back to transport with the grain tank not completely emptied from he previous unload , would spill about a half a bushel of grain on the ground. My new 6600 Sidehill was like this and the 1978 7700 I still have is like this. This was pretty much a non issue as in 1979 the 20 series completely closed unload system came along.
As far as capacity and daily output, if the ground is fairly level, the 7700 will out perform the 6620. Simply larger separator.
Pretty much cutting wheat and milo but some corn and beans. But over all we are talking a 500 acre operation.
It's not a big deal on the cab & dust. If I don't wear a mask when I am stripping cotton I will be congested for weeks. But what you are saying does make sense. The value of the 6620 is just going to drop in my possesion just like the 7700 did with its current owner of 15 years.
not trying to start a color war or anything but have you ever looked at or considered an L-2 gleaner? They are easily the same size capacity and horsepower as a 7720 and are very easy to maintain. You can easily find one under $10,000 with low hours.
This is a tough one. At 500 acres of wheat and fall crops, capacity is not an issue as both machines will can handle those acres without stress. The only question is yields, and if you are growing dryland wheat, milo, soybeans, and some corn in a cotton area, I would expect them not to be real heavy.
Are both hydro or is one or the other variable speed?
Assumption: Both machines are in equal condition, you said clean and straight, which would mean no major or even major/ minor repairs needed to go to the field and cut for 100 hours?
Cab is tight on the 7700, ACs both in working order?
Are the headers in good shape, 224 and a 220 rigids? or flex?
The 224 (24ft) with the pick-up reel is worth $2500-3500 (if in good shape) depending on where you are at and who is asking (just check tractorhouse.com). There is some value in the 7700 purchase even if it blows up, which I would not expect it to if it has been well taken care of and the hours you will be putting on it.
Both machines appear to be priced fairly. If it was me, I would go with the 7700. $6,000 less dollars up front. That amount could be spent on both pretty quick if needing some rebuild. For me, not that much difference in cabs, as long as they are tight and the AC is working (keeping the dust out).
The 24 foot header would be handy and in heavy crops could just take a few feet less cut. If one decided after a few years to get a newer machine like a 7720 or 9500, the header would fit right on (with minor mods). Only two years difference in age, although the 2000 hours is a factor, if both have been maintained equally, the 7700 would last a long time at 500 acres per year (about 100 hours engine time).
You have pretty much answered your question, in my mind, except for one factor: How many acres of each crop and yield are you going to cut?
If the 6620 can easily handle it, then it is a no brainer. The HP is the same (depending on optional or standard) the 6620 has 20 inches more strawalker, so there are some productivity issues that bring the 6620 closer to a 7700 than the 6600.
You also made the comment about the 7700 being worthless "when you are through with it", something to that affect. You have more to lose in value with the 6620 than the 7700, however, the tradeoff is the potential for more repairs on the higher houred machine and if the engine goes on the 7700, well.
The late model 7700s were good machines. The cab for you is probably the deciding factor. Depending on what and how much you are cutting.
We have a 6620 titan turbo run a 920 flex on beans @ about 3.5 mph on 50 bu. beans. Run a 643 with 230 bu corn @ about 4 to 4.2 mph. We put about 900 ac. through this machine per year, it is appraching 4000 hrs.