A single drive won't saturate either BUS, however if you load up your system with a few CDROMS and a couple hard drives, it's theoretically possible that you could soak up the 80MB/sec. Realize that 80MB/sec is a theoretical limit, however, with control overhead you're looking at more like 65-70mb/sec actual data throughput, a number that will decrease slightly with each device using the SCSI bus simultaneously.
I got a 29160 from you a while ago because the performance of the controller integrated into my P2B-DS (based on the 2940) was crippled by two drives transmitting cached data simultaneously. Oddly, the problem went away when 50-pin devices were removed, and I get great performance from the 29160 no matter what I throw at it. If you're concerned with the future you might as well go with the 29160. Or wait until you think you can actually use one, sell your 2940 and pick up a 29160 which will be even cheaper by the time you can really use it.