16 vs 32 ain't gonna make any difference -- your standard ISA com ports the modem use are 16 bit. Overhead? In my testing, ISA overhead is negligible, at least for standard hardware (not talking video cards here) -- complex ISA soundcards might have some effect. 'Course, there are issues about your particular needs -- will you need a PCI or ISA slot in the future? Will your next mobo have an ISA slot? Etc.