It will depend on the particular local modem bank you are dialing into. Some numbers may be v92 and some may not. It'll be determined more from the dialup location than MSN.
I went to the MSN web site -
http://supportservices.msn.com/us/phoneaccesslist.asp
and looked up the local MSN numbers for my area. Some of the MSN numbers are the same as other ISPs serving this local area. So, the Points Of Presence (POPs) are shared by a number of ISPs.
I think some of the modem banks can be upgraded to v92 with just soft/firmware mods. So, if not now - soon.
Ping times? A guess. Maybe just a slight improvement with v92. However, if you have more than one dialup number choice, there may be different network paths and better ping times on one than the other.