Did your height drop with the mach1 springs?Well the springs they are paired with are stiffer than standard Fox springs. I have Tokico Blues paired with Mach 1 springs, and find the handling to be quite nice, while giving me a decent ride.
I think your issue is soft, high milage springs, combined with shocks/struts designed to work with stiffer springs, so the valving may be a little "slow". Like I said before, I'd probably go with a shock/strut that is adjustable, and run them pretty firm, or find a decent spring/shock combo that is pretty matched.