Will idle be affected if one were to use slightly larger vacuum lines or slightly smaller vacuum lines? Barring the obvious problem of a leak due to too large of a size. I was thinking more along the lines of vacuum volume if there's such a thing.

 

No, you should be fine...

 

to what end will you be using these?

if it is some trick to increase hp i think not.....and they wont make good seal with the nipple if theyre bigger....stick to the stockers....