Hi Brushbob,
If you are looking at the Taylormade 580xd you should find that you will get a good deal with the arrival of the
R7 Series.
I can't comment if you will get anymore distance, there are some many other factors to consider.
However you should get some consistancy with a larger clubhead and this is what we all strive for.
If you are not bothered with Taylormade then try the Cobra 440sz this is a very consistant club with a massive clubhead and very cheap for good quality.
Good Luck
Ian.
p.s get one fitted before you buy as shaft flex is very important for direction.