That depends on how you connect extra NIC, I had extra NIC with direct cable connection to backup server and the results were amazing. 

I been using striped backups with 64 files, using the stored procedure below

USE [master]
GO
/****** Object: StoredProcedure [dbo].[sp_fast_backup]  Script Date: 07/10/2013 12:56:10 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
ALTER PROCEDURE [dbo].[sp_fast_backup] ( @dbname varchar(8000)='Database_Name',@fno INT=64, @run INT=0 ,@Path varchar(8000)=null)
AS
SET NOCOUNT ON
declare
--@path varchar(300),
@finame varchar(8000),
@dsk varchar(8000),
@ts VARCHAR(8000),
@cmd VARCHAR(8000)

begin
print ' '
PRINT '-- USEAGE : sp_fast_backup , <databasename>, <no of file>, <run=1/0> , path=<path>'
PRINT ' '

IF @fno IS NULL
set @fno = 64
IF @fno > 64
SET @fno = 64
IF @dbname IS NULL
set @dbname ='Database_Name'
IF @path IS NULL
set @path ='\\10.12.12.25\sql_backups\' + CAST(REPLACE(@@servername,'\','_') AS VARCHAR) +'\'
SET @finame = REPLACE(@dbname,' ','_')
SELECT @ts='_' +convert(varchar, GETDATE(), 112)+ '_'+replace(convert(varchar, GETDATE(), 108), ':', '') + '_FILENO_'
print 'Backup Database [' + @dbname + '] to '
SET @cmd = 'Backup Database [' + @dbname + '] to '
--print @fno
    while 1 < @fno
    BEGIN
        --SELECT 'this is test'
    SET @dsk= 'disk=' +CHAR(39) + @path + @finame + @ts + cast(@fno as varchar) + '.full' + CHAR(39) + ','
    PRINT @dsk
    SET @cmd = @cmd + @dsk
    set @fno = @fno - 1
    END
--PRINT 'out of loop'
SET @dsk= 'disk=' +CHAR(39) + @path + @finame + @ts + cast(@fno as varchar) + '.full' + CHAR(39)
SET @cmd = @cmd + @dsk + ' with copy_only,compression'
    PRINT @dsk + ' with copy_only,compression'
    IF @run=1
    EXEC(@cmd)

end