First of all, Welcome to IDA!!! You will find many opinions here on the Marcum vs Vexilar debate. Take all with a grain of salt… they are only opinions.
Personally, I reviewed the pros and cons of both systems side by side. I did a ton of research. And the opinion I came to was that I liked the Marcum LX5. I just purchased new last year and was extremely satisfied. I love the true color display, the fineline… the dual transducer, the side by side with zoom, etc…. Just overall, I am glad I purchased the LX-5 over the Vexilar. My suggestion is that, after receiving as many opinions as you can, go to a store that has working models side by side and see the differences for yourself.
If you do go the route of the LX5, I have one other suggestion. The prices marked at most stores are going to be exactly the same. I am not sure what kind of discount that the visa says give you, but if it does not cover the taxes or gas money to pick it up… consider purchasing through IDA sponsor Jolly Ann Marine. Wade is the proprietor and is on this site all the time. Last I checked, no taxes outside of Iowa and no shipping. I saved myself about $60-$80 purchasing through him. Wade is a top notch guy… just do some searches on the site and see people’s responses from purchasing from him. I have made the commitment already that, if I am in the market for something, and wade sells it… he has got my business. Go here for more info on his products: Jolly Ann Marine