First New Set of Skis/Boots, Suggestions?

I'm new and have rented for a year. I was told that just about any new set of skis will perform better than rentals I've been using from a local ski salesman.

My first learning experience was at Vail, CO and by the end of the week I was skiing a "hard blue" as described by an instructor in the back bowls and a trail in the Blue Sky Basin.

The rental skis felt quite loose as I tried to increase speed and I would like something more stable. I've studied 3 books by Harold Harb and have found that his technique has worked well for me. The ski salesman recommended the following skis for me and I'd like to know if purchasing these skis will help with stability over the rentals.

Nordica Hot Rod Afterburner XBS
Dynastar Contact 8 or Contact 9
Elan Magfire 8 or 10
Fischer RX Cool Heat

Is a longer ski going to make it easier to maintain control high speeds?

How does the flex index with boots affect comfort and performance? I have read that I should avoid boots that have walking devices because they can flex too much while sking. I was told by the salesman that I should be more concerned with fit than brand when it comes down to boot selection. The rental boots I used just about killed my very bony ankle bones - even after using doughnuts and cutting them to fit. Would Nordica Speedmachines be good start for my kind of situation? The ski shop told me that they would make adjustments to my boots free of charge for a year for the best fit.

Well firstly where will you be using the skis?

On-piste, Off-piste, Pipe, Park?

I'll use them mostly in the western US. I'd like to go to Vail for a few years since it's huge and offers many skill levels. I have a few very small places to exercise in Michigan close by, but want them for the larger mountains.

I like groomed cruisers (with my wife) and I'd like to try deeper powder - ungroomed areas too. I guess I may some encounter crud by moving off piste in changing situations? I'd like to try bumps when I have more experience. I thought these ski choices may give me access to these options.

I'm not interested pipes, tricks, or situations that included lots of time in the air. I feel I may be a little old for the risks of landing hard (42).