Goofy -- not an exact answer to your question but I'll share what I know. I never had an Etec so I can't speak intelligently about it. Also...not a racer so I can't comment about that. My previous sled was an 05 600 SDI that had 10062 trouble-free miles on it when sold. And I do mean trouble-free -- I replaced the throttle body boots/reeds and that's it. Everything else was original (other than the heated grips, which failed in the last year I owned it).
Fuel economy on the SDI was better (16-20 mpg) vs. the 1200 (14-16) but I don't have to feed it 2s oil (obviously costs on that vary). Power, there is no comparison. I can darn near lift the skis with the 1200 (probably could succeed if I altered the suspension setup), whereas I don't think the SDI ever really came close. I'd put the 1200 closer to the 700 class than the 600 class. Guys are saying the 1200 hangs with 800 up to 80-85 or so, and then the 800 pulls away. Like I said, I'm not a racer so I can't offer anything in that area.
As far as handling....I'm just a simple trail cruiser so I haven't noticed much difference. But my wife hasn't complained about the extra weight of hers or that it's harder to handle, so I guess that's a positive!
The 600 SDI was an outstanding, reliable engine (and presumably, so is the 600 Etec). To switch to a 1200 just for the sake of switching, I don't know if it's worth it. But if yours are getting old and you're looking to get something newer, I'd say the 1200 would be worth looking into.