I made 2 one day when the alchemy guild was asking for it for guild pts. I was alch68+1 & smithing38+adv. I failed once and lost a cermet chunk. The other 2 synthesis was very successful. My smithing skill didn't went up at all. So i assume this synthesis could be around 35-40ish. I got fool by the darksteel b/c it is a 51 smithing item. Hope ppl could post something accurate ^^ and good luck with alchemy.
PS, if the guild ask for it, one is more than enough (7440 if i wasn't wrong), the second one was just for profit [sold 50k = 15k(chunks)+10k(ingot)+25k(profitXD)]...mhahahah