I'm curious as well. What's the difference in shaft rpms between these 2? Looked on Tanaka's website and in both manuals to no avail. Looks to me that the 270 was a little faster with the 10" but its hard to say if ice condition/thickness were the same.
I love the Tanaka/Nils combo. I have the 350 and just ordered the 10 inch blade to complement the 8 inch I already have. The 350 has more torque, the 270 is almost twice as fast (41:1 vs 24:1). 270 weighs 12.7 lbs, 350 weighs 17.6 lbs. Since I use 8 inch holes by choice I would get the 270 if I had it to do over again. As with many things in life I assumed that bigger was better, but here not so much. The 270 costs less and is much faster. A friend of mine has the 270, and when we had them side by side, the speed difference was dramatic.
Specs for 350 can be found here
http://www.tanaka-usa.com/main-navigation/products?d=338&p=932 270 is under dills.