Unless the suspension is bothering you, I'd stay with those bikes. As everyone says, put decent tires on, higher pressure, narrower ones, maybe 26x1.5 or so. I've been a roadie for a long time but I commute on my MTB, an older Trek 8000 with slicks. I can't keep up with guys on roadies when they push it, but I keep up with everyone else and usually make them push harder. I'm no youngster at 55 and I think it bothers the hipsters that I can ride faster than they can on their minimalist fixies on my MTB with pannier.