Hi,
I have both they have a simlar tonal balance. However basically the 8tc has around double the amount of cable in it compared to 4tc ( 8tc has 16 strands of cable, 4tc 8 strands of cable). I use 8tc for my biwired floorstander speakers for both the treble and bass/mid connections on my speakers - 4 strands per connection - 4 connections per speaker .
When comparing the 4tc and 8tc. The 8tc has a bigger and deeper soundstage, fuller bass so thats why its probably more suited to floorstanders. The 4tc is probably a little faster and tighter in the bass. Some say the 8tc is a touch warmer, both have a very natural open musical mids. The cables are known for there good imaging, natural musicality and detail. I have compared them to many (chord, supra, IXOS, QED, Eichmann etc) and kept going back to the Kimbers.
I hope that helps
Cheers
Steve.