It depends on what your goals are.

ModelSim goes far beyond functional simulation, but there are a few things to keep in mind.

First of all, if you use one of the manufacturer-specific versions, you'll be limited to the context in which you're working, i.e. the inards of a specific CPLD or FPGA, and, in the case of the FPGA, you'll be affected by the routing, which may or may not be important to you. Often, routing delays exceed the gate delays. The pinout you choose also affects your timing in FPGA's. These effects are much smaller in CPLD's, though they are affected by routing as well, but it's predictable before you assign pins.

ModelSim apparently can't "work its way" out of a failure to meet setup and hold requirements. That means that you can's simulate the beavior of metastability-hardening features, notably multi-ranked registers, because ModelSim just doesn't know how to do that. With some care, you won't be up against that very often.

2 monitors? What for? I use 4 computers on my one 28" flat-panel via a KVM switch. Why would you need two monitors? Isn't it cheaper to have multiple computers? That way you can use Linux, DOS, and Windows at the same time without any of the usual conflicts arising from many of the ways in which people do that on a single computer. The KVM switch saves lots of space otherwise required by monitors, keyboards, etc.

RE