No plant is instantly mature. Older shrubs and trees may have roots cropped for moving. A small tree may outstrip the growth of a larger tree which has to regrow it's roots before its canopy can expand. The answer as to which roses will do best depends also on where you live. In my area antique climbing roses are preferred over new varieties. New varieties are grafted while older varieties are cuttings that develop their own roots. The own-root roses do better with the alkaline soil, heat and occasional drought of my area.

According to Taylor's Guide To Roses climbers are further split into these sub-classes. Hybrid Bracteatas (such as Mermaid) are very large climbers and seldom found in commerce because they require so much space. Hybrid Giganteas are very tender and only grown in warm winter areas. Climbing Hybrid Teas are mostly (but not always) sports of hybrid teas and grow as medium sized, upright plants. Kordesii Climbers are a cross of R. wichurana and R. rugosa that created a new species (R. kordesii). These are medium size, winter hardy climbers with well shaped blooms and dark foliage and are considered excellent for fences and pillars. Large-flowered Climbers is a catch-all class not belonging to any other group. They have medium to large blooms usually in small clusters. Hybrid Wichuriiana Climbers are large, strong climbers with canes reaching to 20'. The white and pink flowers are sweetly scented, but only once-blooming, though some have a pleasing hip display in the fall. Ramblers are the last climbers to come into bloom. They are once-blooming, but extend the season with bright pink, red or purple clusters of tiny flowers. Their pliable canes are easily trained to fences and good air circulation is a must.

Do a search for climbing rose varieties to find which ones might do best in your area. HERE is one link that further allows you to define the search by hardiness zone. Here is ANOTHER general site and HERE is a third.

Geographic location? Soil conditions? Light exposure?

Climbing roses wouldn't be at garden centers if they were all shy flowering - few would buy them. What the nursery person was talking about, in part is how these plants grow, with longer stems that produce larger plants, that being larger take longer to reach full size.

And Ramblers, of course, characteristically bloom once per year. But often this is a mass display, that can be a spectacular landscape feature when the plant is of large size - so even though there isn't repeat flowering within the same year there is no shortage of flowers from these.

Even if you want to make a climbing rose collection with the support being 200 ft. long you should probably inter-plant the roses with suitable companions like clematis and honeysuckle. And something evergreen, like ivies (unless these are weedy in your region, as some of them are here).

And I wouldn't plant the entire length all with one kind unless you find one you really like and want that much of it. Apart from so much room being given to a single variety perhaps not being the most interesting use of the space - there is the possibility of it turning out not to do well there or developing a spoiling problem at some point. Resulting in disappointment with or failure of the entire scheme, whereas when an assortment of kinds is used the risk of this is significantly lessoned (unless conditions are such that nothing tried does well).

Use diligent mulching to improve the post-planting rooting environment including moisture retention. Do not attempt to alter the existing soil except by complete removal and replacement, as in digging a wide trench and filling it with purchased topsoil considered to be of sufficiently superior quality to justify the effort and expense.

Here's a place you can go look for locally demonstrated plants and planting ideas, if you have an ability to get there.

http://sdbgarden.org