I can probably give you a fair answer there. On the basis of pure card tag strength, Red 7 figures to be ever-so-slightly stronger than KISS III for unbalanced use (higher BC, but lower PE). You have to hand it to Arnold Snyder for coming up with the "half-rank" offset concept for a level one unbalanced count. I've talked with him and believe he is a class act.
KISS III however, comes with a fuller and more finely structured accessory package of index numbers (22), and wonging recommendations. This is particularly true if you use the "true fudging" method outlined in the book for betting and enacting the index plays (pgs 172-176).
I see no problem with using your Red 7 count along with KISS's index charts and true fudging method, since the two counts are virtually homogeneous. I believe it would fine tune your play. Just be sure to adjust all indices from an IRC of +9 to -12 (6 decks). etc, if that's how you're currently using it.
And yes, it has to be a close call between performances of the two basic counts.