Making the switch to Windows XP SP3 will ensure your systems are still supported by Microsoft--which is good because you might need a lot of support. Windows XP SP3 is more secure than Windows XP SP2, but significantly less secure than Windows 7. The longer your organization goes without upgrading to Windows 7, the more your organization is going to have to manage the increased support and remediation costs of an operating system that has more critical patches, and is more vulnerable to compromise and exploit.
The Microsoft Security Incident Report Volume 8, released in April of this year, found that Windows XP SP3 systems were compromised by malware only half as much as Windows XP SP2, and a quarter as often as Windows XP SP1. However, it also found that Windows XP SP3 is infected twice as often as the 32-bit versions of either Windows Vista and Windows 7.
Cling to Windows XP SP3 if you must, but buckle up. It's going to be a wild ride.