WinVN is a good online client to use with a 9600+ BPS SLIP connection. This means that it is usable, but will have traits that may be frustrating to the user. Unfortunately, it is very hard to implement the changes that would make WinVN a "perfect" SLIP client. See Sam Rushing's comments about this in the "What WinVN is not" section.
There have been and continue to be improvements to WinVN to better support SLIP (and other environments). The best place to find out about these is the User Manual's section about Reading only UnRead Articles.
[from Greg Monroe]