There is no way you will be satisfied with those amps driving the C5's - they will take all a stout 400wpc amp will deliver and more.
I've owned many pairs of Dyns, but never either of the pairs you're thinking of, so my input is at best an educated guess. I think you'd find the 5.4 a much more flexible speaker, and probably a more "fun" speaker. It has the later driver set, and is much easier to drive. The C5 is, IMO, a classic design, and probably has the potential to be the more accurate speaker.
If you've never heard the C3's, you might look for a pair of those too - I have owned those (a couple of times) and I really love them at their used price. They wouldn't be as demanding in what it takes to get them "right" as the C5's, but would share many of the same virtues.
I've owned many pairs of Dyns, but never either of the pairs you're thinking of, so my input is at best an educated guess. I think you'd find the 5.4 a much more flexible speaker, and probably a more "fun" speaker. It has the later driver set, and is much easier to drive. The C5 is, IMO, a classic design, and probably has the potential to be the more accurate speaker.
If you've never heard the C3's, you might look for a pair of those too - I have owned those (a couple of times) and I really love them at their used price. They wouldn't be as demanding in what it takes to get them "right" as the C5's, but would share many of the same virtues.