I'm not here to judge, or to tell you you're a bad guy. I get all kinds of request so I can understand the temptation.
I can say tho, that if the top art show in this thread is your result of the inspiration below,...someone will get sued...and it CAN be you as well as your printer and more than likely, he's going to want to shift blame when it comes time to pay up. Just say'n. You are no beginner and obviously a very skilled duplicator. With this skill comes some comprehension of artist rights and copyright law. It's not like you've never heard of it.
So, when you say, You were asked to do X for X amount of money and you gotta do what you gotta do. Consider this, The jails are full of the very same reasons. So says the criminal saying he's asked to break in this place by someone and will get paid good for it...and he's gotta feed his kids.
For plagiarism, I doubt you can get time, but you can be sued and lose more work.
Aside from that, showing the comparisons like this and the other biker art, will only get you in deeper troubles. I suggest you step back, reevaluate what you will do for others and reevaluate what you should post...if you do it.
Showing that you are "good" at what you do is great. Showing that you are good at stealing is not so great. It works against you, especially here in this environment where we are all on the up and up and resent such deeds.
I heard saying once by Ben Franklin, maybe someone posted it here. Not sure.
"Better to be be silent and considered a fool, then to prove them right".
Ben Franklin
Now, I'm not calling you a fool. It's just one of those quotes where it really makes sense to not brag about your stealing deeds.
I hope you do well as a result of turning over a new leaf.
Cheers.