Geez... too many things depending one each other and so intertwined
and it can end up being a real slippery slope as well, don't ask how I know :O
Which K3 were you looking at? I ended up with the 79x48 (which looks about the closest to the sc2), which is nice for some sheet work and straight line ripping, the 48x48 seems somewhat popular with folks who mostly work with smaller solid wood.
Charlie might be able to mention some more but the main advantage I see on the sc2 just looking at the spec sheet is the standard 5/8 arbor (guessing it's the same there?), the additional tooling cost for the special Felder blade spec ( 30mm plus the pin holes) can add up a bit when buying blades (having said that I've been real happy with the tenryu blades I bought, the Felder/hammer blade are nice... once you get them sharpened but from the factory they are pretty suboptimal imho).
4.8 vs 4.0 HP motor, actually probably doesn't matter
but the spec sounds nice
Slightly larger rip capacity on the sc2 (ok 2" so very close).
SC2 comes with the ecentric clamp with is a $$$ option on the hammer (
http://www.felder-tooling.us/8head-zub-00320/8b-finish-00b-00420/8head-006110), ditto the rip fence micro adjust and scoring blade (which I have but admit to never having used). You might be able to talk your Felder sales Rep into throwing in at lest the clamp. The fence micro adjust looks cool, and I kind of want it just because but haven't really felt the lack.
Somewhat surprisingly to me the hammer is a fair bit heavier (850lbs vs 600lbs). That can go either way I suppose the american in me says heavier is better because I figure that weight went somewhere, hopefully somewhere useful
.
Also a $$$ option is the lifting bar and rolling carriage, it is worth thinking about how to move either one of these beasts. I sprang for the rolling carriage, but a used pallet jack would be a viable option as well (the hammer at least would want a fairly narrow one to fit between the kegs, unsure on the mm.
Somewhat relevant to both I think is operation of the sliding table, Felder has some fairly nice videos on setup and using it from thier web shop, I suspect that most of it would be relevant to either saw.
http://www.felder-tooling.us/8head-009010/8head-016620/hammer-8head-018810-k3-winner-31x48
I think this is one of the main things folks looking to buy a slider should do is really look at the pluses and minuses of the format. The can be quite nice, but there are a couple of downsides as well, so it's worth doing the research to make sure it will work for you, just imho (I don't regret it but it did take some rethinking my thought processes as to how to use a table saw and I still sometimes find myself doing things in a suboptimal way).