The 3845 is capable of more than 45 Mbps. Its Fast/CEF Switching performance is listed at about 500 Kpps (for 64 byte size packets). In theory, this should support 100 Mbps, duplex.
There are switch modules that will provide the raw performance you're looking for using ISRs, but I don't believe they will provide the combination of performance with all typical ISR featues.
In fact, it's often difficult to find high speed and full features without getting into some expensive equipment.
If your requirement for features are indeed minimal, you might want to again carefully examine the featue set of some of the L3 switches, such as the 3650/3750 series.