My company operates the A321 with V2500, and we always operate with packs off for take-off. The benefit for engine wear has been enourmous, and engine life has been increased by about 30%. We currently have an AD on the A320 regarding Braking performance, and the problem amongst many things is the reduction in Flex temperature. I know on short runways i now mostly operate packs-off, the increase in the Flex temp can be up to 8 degrees, reducing the EGT on take-off by quite a margin.
Packs-off is not an issue with good SOPA's, and anyhow the Airbus FBW reminds you if the packs are off when the Flaps are set to 0, with an ECAM caution.
The pressure bump does not occur on modern aircraft in my experience...