You will be fine. The Kenwood and RF speakers are going to be higher quality speakers to begin with, so the sound difference between them and the stock speakers will be affected by many things, nominal impedance being only one variable in the equation.
If your replacements were the wrong kind (3 way or 4 way El Cheapos, for example) and had a smaller or seriously shifted frequency range, you might try to compensate by adding volume, which may be lacking with higher nominal impedance speakers.
But your replacements should be more efficient and have at least as good a frequency range as the stockers, plus they will not distort until higher volumes than the stockers, if at all. So you won’t be tempted to push the volume higher and higher into distortion land, as you will attain the desired sound level at a volume level within reach of the new, higher quality speakers on stock amp power.
In other words, you’re overthinking it on this one. Install the speakers and go for a drive. You won’t regret it!