I've recently become a complete convert to chainsaw milling with two power heads. Stephen Blair has very kindly loaned me his 72" set up and the difference between it and single ended 088 milling is staggering.
I've long been of the opinion that with regard to chainsaw milling, a doubling of power results in a greater than doubling of cut speed. The difference going from 8.7hp to 17.4hp with the two power heads is a four fold increase in cut speed. Through 45-55" wide chestnut (very knobbly too - a lot of burrs to maneuver around) I was getting a cut rate of 2 to 2.5ft a minute. Conversely, cut rate though 35-40" Oak with one powerhead is usually no more than 1.5ft a minute, and I find each extra inch of with of cut slows things down a lot.
Other benefits - no need for auxiliary oiling, as chain stays well oiled from both ends. Sawmill is far better balanced - I haven't chainsaw milled by myself for a long time now and the even weight of each powerhead makes for a smoother cut.
It's also more efficient in terms of fuel - I cut 194 hoppus foot in 5 1/2 cutting (2.25" boards) on about 13-14 litres of fuel. I would have used 19-20 with a single power head.
Finally, you have to sharpen far less. Due to the much much quicker cut rate, depth gauges can be brought right down (wait until you use your mill again Stephen - you're in for a treat/shock/both!) resulting in fewer passes by each tooth to achieve a set distance of cutting. On wide hardwood I generally sharpen every 25ft of cut with a single powerhead - it wasn't necessary to sharpen more than once every 45-50ft of cut (and that was a wider cut).
So, I'd urge each of you chainsaw millers out there to seriously consider the merits of a double ended mill. I'd wager that most of you who chainsaw mill reasonably frequently do so with a helper to help move the boards. You might as well have two powerheads, save yourself 75% of the cutting time, 30% of your fuel, 50% of your sharpening and all that HAVS exposure!
Here are a few pictures from the cutting of the sweet chestnut. This was the first length, which was quite clean and free of burrs.