Go with the lighter machine and be kind to your body. I sit here with a v. sore back, with a 5 hour trip ahead of us in a day or two and wonder how I'll manage. I carried heavier than I should have plants the other day. My own fault.
Be kind to your back. Don't put yourself in harm's way. Go with the lighter-weight machine, which is, I hear, a very good model. Sounds like you'll have the best of both worlds with the Janome: quality and comfort.
Blessings,
A.