First off, welcome aboard; glad you found us here!
The over-arching difference between all GA and GS guitars (the x14 vs x16) are:
- GS is slightly wider at the lower bout: some find this minor difference unobtrusive while for others it is a deal-breaker
- GS' larger body produces more bass; the guitar's overall voice is "bigger" and with low end more dominant than its GA sibling
- GS uses medium gauge strings, and the top is
braced for it as well. So the mediums add to the string tension and "stiffens" the playability, as well as thicken up the notes, including the treble strings. Again, this is either a minor adjustment for some, or a killer for others.
And the point of being
braced for mediums is important, too, as you "can" use lights on a GS, or mediums on a GA: it's safe, as per the factory. But the tops are designed from the get-go for med and light, respectively. So while it is completely kosher to use the "other" gauge, the tone may or may not be what you expect since the soundboards are braced --thus tuned-- for "its own" string set.
So those are the generalities between the GA and GS. But with each different wood combo, I think it matters much as each wood brings a different flavor and tonal bias to the table. But as you're asking for opinions, I'd personally suggest a 614 for you.
1. You have an HD 28, which is one of the guitar world's sonic cannons. The 616 (likewise the proverbial cannon) would likely be somewhat sonically redundant. Different in tone from your HD28, yes, but why have something so close, IMHO.
2. the revoiced 614 would play lighter and "faster," and I personally think the revoicing of the new 600 series makes the GA and GC (the smaller body) the prime benefactors. My ears "liked" the 616, but preferred the balance of the 614. Really great vocal balance across all strings on the 614, and would be a nice contrast to your Marty, IMHO.
Hope that gives you some food for thought! Post pics of your victory!
Edward