I don't think the MTNL Mumbai network supports HSUPA (or at least most towers in Mumbai do not), so the max upload speed would be 384kbps. The BSNL network does support HSUPA, so when the MTNL sim is used on the BSNL network, one will get higher upload speeds.
Can anyone confirm having got more than 384kbps upload speed within Mumbai city limits? One of the speedtest results above shows connection to the Thane server, most probably through BSNL.