Nimbostratus
Employee
ASM is only compatible with standard mode virtual servers; IP forwarding routes the packets rather than handing them off for additional processing. The effect of Performance HTTP will depend heavily on your traffic profile and application, so I cannot really comment on it. ASM performs significantly more processing than a standard VIP. Given that, inefficient iRules could have more of an impact that using the HTTP Performance profile. Without knowing more about your environment or volume of traffic I cannot comment further.
Are you having performance problems, or just trying to optimize as much as possible?
--jesse