i have the same sled and run 350's in mine i could probably ride with 340's but it's below 20 degrees a lot here so i wanted to stay safe.
a lot of other guy's on here run 340 and sometimes 330's just keep going down and check your plugs as you go.
Where I sled: Now....Gulfcoast and back bay on a jet-ski
I had the same sled and would run 330s above 0 and 340s below that. Just keep an eye on plugs when it's real cold. If you have a good set of EGTs, which I had installed, that will give you feel for what's going on. 340 or 350s are a good safe all around main though. This is of course if you are all stock with no aftermarket pipes or anything and good for elevations 0-2000 or so.
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