Last time I tried something like this I got some... interesting results. The candi syrup I used (snick's double cooked from here http://www.homebrewtalk.com/f12/20-lb-sugar-jar-yeast-nutrient-114837/
) was massively over-powering and I only used about half a pound for 5ish percent of the grainbill. It was actually pretty damn undrinkable early on and even after extensive aging wasn't much of a stout. Meanwhile, the same recipe minus the candi sugar has produced very pleasant results. I have however used special b in very, very excellent stouts in the past and found it gives the flavour I normally look to candi syrup for in this situation without being so damn in your face and overbearing. Just a little easier to control I guess; much easier to get a subtle result with. Might just be a result of my candi syrup, but I'd still advise you to err on the side of caution.
I'd either limit the candi sugar to maybe two or three percent of the grain bill and drop the special b, or drop the candi sugar and leave the special b as is. Having both in there is redundant either way. I'd also personally massively increase the roasted barley and throw some oats in there instead of the wheat but that's just my personal taste.