I've had a good run with 270, but always felt like my 30-06 was easier to shoot. What with 3 6.5's, I had all but decided I was out of the 270 business when I ran across a 1963 Winchester 70 at a price too reasonable to pass up. And go figure- this beat up, bottom of the barrel pre 64 is the best 270 I've had to date. Since I can't seem to get away from the cartridge I guess I better give this a try.
OP- If you ever retry the Sierras please post your results. Were I you, I would have given that load one more test as your groups were round and not stringing or doubling.
Well done and good shooting!
