The Switch to Native mode

I have a small network with 5 Win2k Servers and 2 NT 4.0 servers which are member servers. 3 of the Win2K servers or DC. I am running Exchange 5.5 sp4 on Win2K and SQL 7.0 sp1 on NT 4.0. I have all Win2K Pro clients with maybe one Win95 client. If Iswitch to Native Mode will legacy clients still connect. Will it improve performance on the network? I will not be adding any NT 4.0 DC in the future. Should I do it when everyone is logged off? Other considerations? THanks.