When most of the classical repertoire was written, there was no Boehm system clarinet, which is more accurately the Klosé / Buffet system. One resource that I recently referenced, "The Early Clarinet: A Practical Guide" points out that many orchestra players were still using Albert system clarinets as late as the mid 20th century.
Whether or not the classical repertoire is easier with a Boehm clarinet or not, it appears to be easier if one has an A clarinet as well as an Bb and generally an orchestra player is required to have both. That seems to indicate that there are keys in the classical repertoire that are not Bb Boehm friendly. Which system one uses might be less important than the key the music is written for with the classical repertoire. Germans and a good portion of Europe favor the Oehler system for classical music so how bad could it be? I think for classical, it is a matter of experience and personal preference.
Most of the bebop and jazz is written in what some of us call "horn keys". Those are keys that are "home" keys for brass, saxes, and Bb / Eb woodwinds. Those keys are always going to be easier to play with a Bb soprano clarinet. I don't have enough experience with Albert or Oehler to know if there is a great advantage to a Boehm over these for this music, but I can definitely say that there are some keys that are not as Bb Boehm friendly as others.
What I have found out about Boehm is that I prefer the 7-ring version over the more typical 6-ring. That 7th ring makes certain key scales and arpeggios easier to move through if you know when to use it.
If you are bound to the Albert system by starting with Turkish music, then it will probably be easier to learn the Oehler system on top of that because like Dave pointed out, Oehler is mostly Albert with some refinements and extra keys.
Be aware also that the key system is not the only difference between Boehm and Oehler. Boehm clarinets use a mouthpiece design that evolved in France and Oehler uses a mouthpiece design that evolved in Germany. These are significantly different in the way these play and the reeds for each are cut differently. I would suggest that you compare the Turkish clarinet mouthpiece to the German mouthpiece and the French mouthpiece to see which is most similar to a Turkish G clarinet. The type of embouchure technique you learn is just as important as the key system, if not more so.
