In A320 slides & doors
 

As far as I know in 777 as a pax or crew you can open the doors & slides till 68kts
Is there any information about A320?
Generally captains say you can open while inner and outer pressure are equal.But I need book support is there any ?

Air India managed to do it while taxying recently.

http://www.airlive.net/wp-content/up...017/08/055.png

NEWS Air India crew accidentally inflate emergency slide while Boeing 777-300 still taxiing | AIRLIVE.net

Are you looking for wind speed or taxi/ground speed limitations?

A320/321 wind speed limitations:
PAX doors 65 kts
Cargo doors 40 kts, or 50 kts if nose into wind or doors on leeward side.

B777 & B787 have flight locks fitted to the pax doors. At 80kts IAS the locks engage during the take off roll. After landing they disengage below 80kts IAS.
I don't think the A320 series have a similar system.

I could be wrong.

Those are the speeds above which you shouldn't open the doors (which is not to say you can't).

Depends how you interpret 'can' in the OP I suppose; do they mean 'Allowed to' or 'Physically possible'? The OP talks about a speed in the first line and a delta pressure in the second, which adds uncertainty.

I mean physically possible ? What if I try to open the door at 700 ft ? Because delta P is not above 1 Psi at that altitude