As you may have seen in other posts, the UD client will only use one thread/processor, or one processors worth of your machine (the system may share it out across more than one processor). As your machine is a server, which you want to be responsive to sudden client demands, this may not be a bad thing.

BOINC, on the other hand, will use as many processors as you want (actually up to a max of 4 I think). This is configurable via the web settings page. BOINC will simultaneousely run a number of workunits to match the number of processors that you have given permission to use.

Remember that each workunit running will need its own portion of memory, so in actual fact, your seemingly large memory of 1.2 GB is actually not so big to run 4 workunits simultaneously. FAA units use 271 MB each. HPF use much less, so it depends which projects you intend to run as well. In practice, if you opt to run both, you will have a random mix of each project running at any moment. If you ever end up with 4 FAAs, you MAY find the server becomes a little sluggish to respond to a sudden rush of client demands. Servers often sit for ages doing nothing, and then become busy. In the event of a sudden demand, BOINC will of course relinquish your processors and memory, but it takes a little time. Whether or not this is a factor, depends on you and what your server is for.

You could also use time scheduling to run only during the periods that you know that your server is not busy. This is all or nothing, unfortunately. It is a pity that it is not possible to schedule the NUMBER of processors in use as well. As multiprocessor machines become more common, this may get added to BOINC's features.

I think you should experiment.

Happy experimenting!