I have only had them on plastic so far. To hot to climb outside in Oklahoma. I am ready to get them on Oklahoma Granite.

Five Ten says that they should stretch out 1/4 size through use.

So far at the silo gym that I climb at (Rocktown in Oklahoma City) all of their natural pockets that are hammered out of the concrete. The shoes hold them well. I haven't got the best smearing performance so far, but we will see what a full break-in brings.

The Stealth Onyxx Rubber feels a lot firmer than the Stealth C-4 rubber.

I also own the 5.10 Spires.
My spire's are an 11 and are comfortable for all day wear. I purchased size 11 Anasazi VCS They are considerably tighter in the toe-box and can only go 1-2 climbs with out taking them off.

Overall they are an excellent second shoe to have when more performance is needed.

These shoes are honestly my all around favorites- nothing you can't climb in them. They particularly excel at thin face holds- super sticky from day one. It is true that the heel has a little unused space, but they steel heel hook great. I love them for climbs that really have a lot of variety- a little crack, a little slab, a little steepness, etc.
http://www.lookingglassoutfitters.com/shop/product.php?productid=38&cat=33&page=1

This is my second shoe. I bought the Mad rock flash's loved them but they died on me after a year. I am now wearing the anasazi velcros which are great shoe overall and are comfortable also. The rubber is still great the only problem is the heel which is a little bit large. A more fitting heel is the only thing stopping this shoe form being a 5

these shoes are great.. size them a full size down from your street shoes. you don't need to size them very small cause they don't stretch very much. great on very small foot holds. the rubber is radical.. very sticky..! and the new heel is great, it's like having another pair of hands. hehehe.. excellent in any type of climbing.. easy on and easy off! a great shoe..! five ten shoes are really well designed..

I got these shoes shortly after I started climbing and hated them for a long time. After breaking them in all the way, and after my toes got stronger I realized how awesome they are. They do everything, great for edging, smearing, toe and heel hooking, and jamming. They are now my go to shoe.