I looked at both of these machines plus the LaserFibre Eco. Here are my take on them.
Revo4000. Nice machine, great support from Alpha, everything is very solid the only thing that is questionable is the turntable. I believe it is made out of bent steel. I also believe that the clamps are a little better on the Alpha than the Gamma.
Gamma ST II. The turntable on the Gamma is more substantial then the Alpha. If you are going with this machine, make sure you get the newer model with the all-metal clamps. I have called 2 vendors and they gave different answer. ATS is probably your best bet.
I was set on the Revo4000 but it is on back order and would not be available till 1st or mid of April. Gamma is also backorder and will not be available till the 26th of this month.
I went instead with the LaserFibre TT because I can get it sooner. The cost maybe more but after talking to LaserFibre-Tim Sullivan, I came to the conclusion that the TT was a better machine than both the Revo and the Gamma. They do not skimp on the turntable or the clamps. Talk to Tim, very nice guys. Will never push you one way or another, just gives you the facts. He actually said both the machines, Gamma and Revo are very good machine just like what is posted here on the forum.