I don't have a 123 a lot of guys here use straight 30w if stored indoors and given 5 to 10 minutes to warm up. That being said, you should be just fine using 10-30 in the winter. And, btw, oil shouldn't really lead to slow cranking. Winter is hard on batteries so now would be a good time to invest in a battery tender. I got one from Farm and Fleet for $15 (something like $20 normally) on Black Friday and now if I know snow is coming, I put it on my machine the night before so I've got a good strong battery in the morning.
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-Ryan 
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