The short answer to your question is 'it depends'. Regardless of the application, what is the most important is the actual performance of those systems. It has been my experience that approximately 90% of the time, a system is a decent candidate for virtualization. However, that last 10% can really be what does you in. Most of the time I see that 10% be primarily 2 factors - page file usage and disk i/o. Occaisonally, you will see a box that is used really well and shouldn't be virtualized as it is ok on bare metal.
What I would suggest is that you either commit the time and resources to evaluate your systems performance and then do some thorough testing, or pay someone to do an assessment for you. The latter may not be cost effective as you only have a few systems. Either way, what I wouldn't do is just wing it. 
Good Luck!
SrTim
