Hi Dan,
I thought this info might be useful for you. I found this on Brushwood Nurseries web sight for your clematis:
'Pruning- Candida is a Group 2 (B) Clematis, which means it begins flowering in early summer from last year's growth as well as flowering later on short canes from new growth. While pruning is not necessary, it can be used to shape the plant and encourage more flowers on new growth. These can be pruned in spring before new growth begins for a more floriferous show later in the summer or pruned after spring flowering so that the earlier show of larger, but fewer flowers can be enjoyed. Look for fat, healthy buds on sturdy branches, about a third down from the top and cut just above these healthiest buds. Remove dead or damaged branches any time'.

How well-established the clematis is -- and therefore how large the woody trunks - will have a bearing on how well the vine will respond to this kind of treatment. In general, vines that have developed true woody trunks (as opposed to just a thickening of the lower stems) do not respond well to hard pruning into this wood. 'Hard pruning' on vines like this is typically restricted to cutting back to the third set of buds from the base, which with larger trunks, can be as much as 12-18" (or more) above the ground. IOW, like many other woody plants, cutting back into bare wood is not a good thing :-)

That is not to say the vine won't respond favorably. The best you can do is wait and see. If it does come back - and it may be slowly and from the base/root crown - you have at least learned that you might want to take a lighter hand at the pruning chores. Type 2's can be hard pruned - many growers treat them as 3's for pruning purposes, thereby delaying the initial bloom period slightly - but hard pruned with consideration on how old or how established the vine may be. Cutting back to 6" is a bit severe for any clem more than 2 or 3 seasons in the ground.