You might check the backup history to see what your throughput is for each database, find the worst one and work from there. I modified this from Brent Ozar's script here[/url]:

SELECT bset.database_name,

YEAR(backup_finish_date) AS backup_year ,

MONTH(backup_finish_date) AS backup_month ,

CAST(AVG(( backup_size / ( DATEDIFF(ss, bset.backup_start_date,

bset.backup_finish_date) )

/ 1048576 )) AS INT) AS throughput_MB_sec_avg ,

CAST(MIN(( backup_size / ( DATEDIFF(ss, bset.backup_start_date,

bset.backup_finish_date) )

/ 1048576 )) AS INT) AS throughput_MB_sec_min ,

CAST(MAX(( backup_size / ( DATEDIFF(ss, bset.backup_start_date,

bset.backup_finish_date) )

/ 1048576 )) AS INT) AS throughput_MB_sec_max

FROM msdb.dbo.backupset bset

WHERE bset.type = 'D' /* full backups only */

AND bset.backup_size > 5368709120 /* 5GB or larger */

AND DATEDIFF(ss, bset.backup_start_date, bset.backup_finish_date) > 1 /* backups lasting over a second */

--AND bset.database_name = 'MyDatabase'

GROUP BY YEAR(backup_finish_date) ,

MONTH(backup_finish_date) , bset.database_name

ORDER BY @@SERVERNAME,

YEAR(backup_finish_date) DESC ,

MONTH(backup_finish_date) DESC

Regarding compression you might want to check what build you are on for your instance. If you are running SQL Server 2008 (10.00.xxxx) then backup compression is not supported unless you are running Enterprise Edition. SQL Server 2008 R2 allowed this feature in Standard Edition. You might also note that you are running an unsupported version of SQL Server.

Microsoft has an article on Optimizing Backup and Restore Performance in SQL Server that might be worth reading as well.