The single-rider line is the only way to go for Splash Mountain. I've done it several times and the longest I've had to wait is about 10 min. Once my sis and I went in the single-rider line and although we didn't get in the same log, we were one right after the other. I often get off and go right back on. I'd never wait 45-90 min.
The only downside I see to single-rider on Soarin' is that I've always been on the bottom row and in an end seat. However, sometimes the "end" is actually the inside end, which is really close to the middle. Again, I don't know if it'd be worth the time waiting 60 min. just to have a chance at the other rows (no guarantee!). As far as wait-time, I've never waited more than 10 min.