Dave,
I think if I were you, I would wait until your Ventura arrives and you have the oppertunity to shoot it a lot before you decide on your next bow. If you miss a good deal on one now, chances are that another will come along. After you have shot your Ventura for some time and developed proper form, along with getting your muscles used to drawing a bow, you could consider a heavier bow.
Shooting a light weight bow is great. You can shoot it longer before you start getting tired. Once you begin to get tired, it seems like your form starts to degrade and you might pick up some bad habits. As soon as I feel that I am getting tired/sore, I stop shooting.
A great book on shooting is "Shooting the Stickbow". I highly recommend it:
http://www.shootingthestickbow.com/
One other thing to consider, it seems like older Martin Bows were marked lighter than they actually were. I have a 10 year old Dream Catcher that is marked 50# @ 28", but actually measures 55# @ 28". The newer ones seem much closer, usually within a pound of what is marked. It is good that you are measuring them at your draw length as this is what you will feel. Also, when measuring, you might want to take note of what they are at 28" & 29" also so you can determine how fast the weight is increasing (stackinig). I've seen bows that increase anywhere from 2#/in. to 5#/in.
Good luck!
Dean