The noise level tends to depend on IAS. The higher you fly, the lower the IAS for a given mach number, and the quieter it is. I haven't noticed any difference between the older and newer CRJs.
I use the Telex 750, tried it with earplugs but can't stand having them in for long stretches. I started out using DC's, but they can be very uncomfortable on a long-leg, long day. Generally, the captains I've flown with who use DCs will take them off above FL180. Overall, I prefer the Telex.