If you're talking one or two packages, I would risk the mixing of ports and packages. For example, on one aging machine, I use packages for everything except the dwm window manager, because I use a custom config file which requires the port.
On another machine, where I was a lot more careless and broke things by excessive mixing of ports and packages, synth managed to fix everything. However, (and of course, it depends upon what port you're planning to build), there's a reasonable chance that using packages and one or two ports isn't going hurt. Note that I said a reasonable chance.
Anyway, let me add to the praise for synth, but again, if it's only one port, it may be alright. What port is it? If you run portmaster <pkg_name> if it's already installed (or portmaster <category/pkg_name> if it's not yet installed, how many packages does it say it's going to install, upgrade, or remove? If you get something where it's going to say, change perl and every perl related package you have, there's a good chance that it will break something. If it's only going to change the package itself, and not affect any dependencies, it probably won't be a problem.
