[J.Kydd]

Going to be sending a pair of Katana velcro up to Llanberis for a re-sole, but I'm really not that keen on Vibram's XS Edge rubber.

I've never used 5:10 shoes, so have no personal experience with their different compounds. I can choose between C4 or Onixx
Is anyone able to give me a definitive answer of the difference?

I use them in a totally all-round way. Indoors, sport climbing at Cheddar & Brean and for some slabby boulders

[duncan]

C4 is medium soft and sticky, great in colder conditions, probably the best all-rounder. Onyx is stiffer and a little less sticky, like XS-Edge, more of a warm-temperature edging rubber.

[tk421a]

Have you already asked Torquil?

[dave]

I think any differences between C4 and Onyx are marginal at most. Condition of the boot/holds/edge/temp have  a much greater bearing, if there is a difference it is swamped by environmental factors for me.

[Drew]

I take it you've seen Torquill's thoughts on the different rubbers?

Basically he says that C4 is the stiffest that he uses, but bear in mind that the C4 is 20% thicker than the XS Grip2.

Personally having used all of the 4 in question, the only difference I've noticed is that Onyxx has sometimes rolled off tiny edges, where the other three haven't. Stickiness? Well I still maintain that my Red Chili Dos Equis were stickier than my old Anasazi Velcros, but I think they just fitted me better.