Phrase, exact matching and plurals

I'm confused

[twelver]

I have one ad group with about a hundred keywords. I took out my best four and put them in a separate ad group. They are basically the same keyword listed 4 ways; "widget case" "widget cases" [widget case] [widget cases].
All four get decent impressions and a CTR of between 3.5 and 5.0 %.
Does it make sense to keep them separate? Should I reduce these 4 to just one or two? Would "widget cases" capture all the impressions the other 3 would get? CPC is different for each with [widget cases] being the lowest while pulling in the highest clicks.

[specter]

Hi,

Does it make sense to keep them separate?
Should I reduce these 4 to just one or two?

This depends.The only reason that justify to keep them separate is that if the keyword is present in the ad text it will be put in evidence when a search is done,making your ad more visible.

Would "widget cases" capture all the impressions the other 3 would get?

This is very probable.