I have been riding motorcycles for 40 years. The best way I can answer your question is to tell you that each bike is different. They each have their own little quirks. Both bikes you list are cruiser style, so besides the engine being more powerful and the wheelbase being longer on the 600 than what you currently have, you will not find them to be all that different. Check out the VLX for fit-you know reach to the handlebars, seat height etc. Make sure it is a good fit. Also bear in mind that most bikes can be adjusted-handlebars rotated back, seat padding cut down etc if you are not comfortable on the VLX.
I would also suggest checking out www.womenonwheels.org . We have chapters in most states and in some foreign countries and if you go to a local meeting, you can talk with other women riders, who much like yourself are on the shorter side. See what they ride and what mods have been done. Most chapters also have group rides and a lot of fun.