Well, I've taken the Eric Canete challenge. I figure most people who come here know who he is, but it you don't he's one of the best.
Eric recently did a demo on his inking process and talked about how he tries to keep his commissions at around 90 minutes to finish. He started doing this at his day job, where he could draw. The more he did, the more he learned about his speed, and the better he got. He eventually ended up doing a lot of work for Marvel.
I think it's pretty inspiring, so I've decided to take on that challenge in addition to my other stuff. I started this Tuesday, and it's been going well. I think it's making the other stuff I work on better, so I plan to keep it up. I'm finding that focusing on that 90 min timeframe is training me to stay more focused on ALL the drawing I do.
Here's my first attempt with the Punisher at 90 min.