I like the colors of both of these and might get them next spring. Are there any cons to either of these plants?

I have them. The only negative thing I have to say about them is if they aren't grown in full sun, they can get kind of stringy and require cutting back to be bushy. Otherwise, a very tough plant , very good for bees and hummingbirds.

Have any idea how they will grow if kept in three gallon pots?

No, mine are in the ground. Since you live in Florida, I would think they would do great in pots, and that size should be good.

Black and Blue is a tried and true older variety. It has been bested by a number of newer varieties that have much better foliage and growth habit along with more and earlier flowers. More tolerance for less than ideal exposure (sun) as well.

Sometimes the newer varieties are released to increase a grower's sales. In this case the older variety is truly inferior to the latest and greatest.

I am getting different info from two websites to n salvia van. One says it blooms in late spring and the other says it blooms in july.

Salvia splendens van houttei bloom year round in frost free climates. When it will start in colder areas is a function of plant maturity/size and the weather. A month of war weather and a good size plant = blooming.

What are the newer varieties of Black and Blue ? I live up here in NB, Canada and managed to finally get a bedding plant of B&B last year and loved it . None available this year , generated some seeds last year and some did grow but of course not true. Are all these plants only available as bedding plants. Living here there is no supply of these varieties of plants. I love salvia/sage and the deer here ( huge problem) do not touch them so love to plant different varieties . Can anyone help with seeds that I can grow myself .