I'm not too sure about fast leveling, but I have a Assassination/Subtlety rogue and it's really fun. I've read up on rogues from a few different places like wowwiki, and have heard that Combat is best for fast leveling because of the survivability that the talents give you with the added dodge and parry chance...especially when taking on multiple mobs.
I've leveled my Undead rogue up to 35 (only casually playing off and on, so I can't talk about how fast it's been) but have had no problems soloing quests with him. It takes a bit more strategy and timing with choosing your victims and choosing when to attack, but it's been very enjoyable. I know a few people that have Combat rogues and they say it's kind of dull with the constant "backstab, sinister strike, sinister strike, eviscerate" combos. I think it's more fun and having the enhanced stealth from "Master of Deception" and "Camouflage" makes up for the extra time you take on the pure grinding quests. It allows you to just stealth past mobs (especially in caverns and confined spaces where sneaking past mobs would otherwise be imposible) that don't have anything to do with a quest and just go straight for the quest objectives.
So, combat rogues might make questing and leveling go a bit faster, but personally i go for more fun over speed. But that's just my personal opinion
I would like my build, but I'm not sure how to save it and link it to the forums. When I get to 70 I'll be a 30/0/31.