I'll take stab, but describing how guitars sound is so difficult for me. I never feel I have the ability to adequately express what I hear, or do justice to it, especially in light of how eloquent and even poetic some of our forum members are.
First, let me say that both the J-45 TV and the SJ TV are fantastic guitars. Any Gibson lover would be pleased to have either.
That said, there's something magic about the J-45 TV I was fortunate to get (appologies to Gillian Girl). I've often heard guitars like the J200 compared to grand pianos. Well, this particular J-45 TV is the grand piano in my collection of slope shouldered Gibsons (which also includes a red-spruce topped J-35 reissue, an AJ, a short-scale maple AJ, a rosewood J-45 Vine, a J-160E Standard, J-160E Peace, and three MIJ Epiphone Texans, which I consider in the Gibson family by virtue of both their lineagee and their quality). This J-45 TV is clear and strong and balanced in every register, particularly in the bass, and it has great sustain. It's clear as bell when fingerpicked even lightly, and it thunders when strummed hard.
The SJ TV's bass is good and clear, though not as strong, round, or complex; it has less of a deep, reverberating, and authoritive quality. It's top end is smidge less sweet, too. It's sound overall is drier and more percussive, and it likes, or even needs to be driven a little harder. Don't get me wrong, it's a wonderful guitar. I'm just trying to describe it in contrast to that particular J-45 TV I have.
Remember, the two have some structural differences. The J-45 TV has an adi top and the high, thin braces on the back. The SJ TV has a sitka top and squatter, chunkier braces on the back. I have not looked carefully at the SJ TV's top bracing or location, so only assume its the same as the J45 TV/AJ/J35, but I don't know for a fact. The J-45 is a 2008, and the SJ is a 2009, I believe.
Hope that helps in some way.
Red 333