You'd have to train it horizontally, as otherwise, the shoots will go up and over the 6'. Otherwise, yes, it's a fast growing climber - does the area get enough sun for it to flower well?

Have you thought about Clematis cirrhosa in between Jasmine plants? They're evergreen and would extend the period of interest, as they flower in winter. 'Freckles' is a good one...so is 'Lansdowne Gem'. No pruning required!

Position is very important. A sunny, south-facing aspect will dictate a totally range of options from a shady, north-facing one.

My first choice would be the beautiful, fragrant and vigorous Clematis armandii, and I agree with Spritzhenry that Clematis cirrhosa would be a good choice too, as would Passiflora caerulea. Hydrangea seemanii is another good option and is also self-clinging so wouldn't require the support of wires.

A stretch of 50 feet is large enough to grow a real array of lovely evergreen climbers, and not all would need to be vigorous, so definitely think of it as an asset rather than a problem.