Nah don't cap it especially on axe or you'll make your players quit. I've known a person who had to buy x3 axe parts just to get up to 8x DD. if you guys change the dd all of a sudden, then all these people who already managed to get the nicer dd will quit.
You guys should also put shiny hp options (1000 hp ones) on sale in im. Everyone else has 1xxx hp and we want to have like theirs too.