I would address your questions to Bob Perry <firstname.lastname@example.org> the designer of the Saga. He has designed a lot of ''serious blue water cruisers'' and seems to speak quite candidly about things.
I have had the chance to observe the Saga 43 underway in a number of conditions. They are quite fast on a reach in moderate conditions. They are better than most heavy cruisers in light air and beating but compared to a coastal cruiser are not especially good in light air and don''t point as well as I would have expected from a narrow waterline boat. The one that I am most familiar with has a shoal keel and that may be the problem. They also seem a little tender but that may have been more of a product of sailor error, carrying too much sail for the conditions.
I believe that they were developed as a performance long range cruising boat but I have never been convinced that they were successful as such. There just did not seem to be enough storage and the like for serious long distance stuff.
I am not a big fan of their rig. I know what they were trying to do but I don''t think it has been successful. The narrow slot between the two headsails means that you have to roll up the forestaysail (genoa/reacher) every time you tack. I think they would have been better off going with a fractional and bigger mainsail and then using a more conventional Code zero with a sock.