I'm no expert, but the sabre is faster in a dive. The mig will be harder to handle at near mach. I THINK that the mig is better at climbing. The mig doesn't have quite as fancy of a gunsight. The mig has bigger ammunition (the cannon).
Other than that they seem quite similar. When in fights they feel very well matched in my opinion. I love the mig and if you like the sabre I would recommend getting it for a ONLY slightly different experience.