That's a fairly beefy server and a fairly small Exchange environment. You don't mention the box's RAM and disk configuration but, assuming they're not unreasonable, you should be fine to run E2K10 in a VM.
Exchange 2010 has radically decreased I/O requirements as compared to Exchange 2003 (so long as you feed it enough RAM to let it cache effectively).
For a basis of comparison, I'm running Exchange 2003 (w/ all of its crappy I/O perf) at one Customer site w/ 250 users and a similar email load in an ESXi 4.1 VM on an R710 w/ a 5500-series Xeon. I'm using 15K SAS DASD in a couple of RAID-10 volumes (one for the database, one for the logs) and it's running acceptably (for Exchange 2003). RPC latency isn't bad and users aren't complaining about "Waiting for Exchange Server..." toast messages.
In a few weeks I'll be putting Exchange 2010 up an indentical box to that one, as a VM ( when the Customer buys the licenses). I'll be 64-bit, then, so I can give it 16GB of RAM (rather than the 4GB I'm stuck with on E2K3). I anticipate no performance problems given the benchmarking of the box I did in pre-production. Benchmarks aside, E2K3 is an I/O pig compared to E2K10. For my purposes I decided that if E2K3 would run acceptable E2K10 certainly would.