Ech NMM! Stay with metallics... well... Unless you like the lame cartoony look of it!
I think this guy kicks ass!
Though the bolter does need a bit of *something* to break it up as stated before.
Over all I like the conversion. Interesting use of the Emperor's Champion. On the negatives... I think your black highlights need to be a little more subtle, maybe an inbetween layer. Also the bolter could use something other than boltgun metal as a color. Somthing to break up the weapon into pieces. Gold is nice, so is your skull work. Looks like you did a good job on the gems. Base could use something else though. Nice job overall.