Just say it like it is, without putting a slant on it - A's response rate was 0.6% higher than B's.
I don't care if the results are significantly different, if the difference between the two samples is so small.
citing an absolute difference isn't very useful when you're talking about differences in conversion rates.
* 0.6% -> 1.2% is a 0.6% bump.
* 49.4% -> 50.0% is a 0.6% bump.
it sounds like you're saying that if someone increases their landing page conversion rate by 1% (from 1%) you'd rather hear that the conversion rate increased by a point.
the business owner is probably more interested in the fact that their revenues doubled.
However, the relative difference (4.9%) is the relevant metric to be looking at as noted by "ezl" in a comment.