As an saxophonist turned full time oboist I actually want to expand on your list so I'm going to add my opinion and do my best to order them. Yes this is only my personal opinion, however I think it is a solid one .100% agreed. Sax fingered oboes are dreadful. Steer clear at all costs. Same with single reed oboe mouthpieces. If you are really interested in an oboe, buy the very best model you can afford and above all take the advice of a good pro oboe player. There are maybe 10-12 good oboe makers, and about 6 absolutely top-class:-
come to mind, in no particular order. There are some excellent lesser known instruments and up-and-coming makes too, so this is not an exhaustive list by any means.
Hiniker (if you can find it!)
Laubin (7 year waiting list but a GREAT oboe)
Keep in mind that only in America is Loree a top choice. In 1994 at the Oboe Blow Out they did a 'blind oboe' test. Rigoutat was at the top by far with Loree at the very bottom.
Sometimes I wish oboe only had as many viable brands as saxophone...classically speaking
Check out this for more information on some of the other brands
and most importantly of all...be sure to try the oboe you want. If you're going to invest the time into doubling (or converting) to oboe you want to get the instrument that you enjoy...not what other people tell you to play.
As far as the original topic...i would be very worried about a saxophone system oboe. How would the extended range work? Could it still reach the double C? Would pitch tendency change? The fact that you would lose the 2nd octave key (side key) would be a *nightmare* to me. You'd lose all your harmonic fingerings (scary!) I guess I'm probably a little more oboe-y than the typical doubler but i'd be scared of those things.