By the way, does anyone know what is the max ping tolerable to be able to play a competitive PvP without suffering from connection delays in a way that would affect the outcome of the fights ?
And, also, whether below a certain ping it does not really matter in PvP as far as affecting a fight's outcome.
I would say it's pretty hard to give an exact number, as it's a feel thing. One thing I can tell you is if you are using the enhanced client you can play competitively with a much higher ping than you can with the classic client. With the classic client as your latency increases your movement speed decreases, so a high ping with the classic client puts you at a serious disadvantage.
I've already posted this, but what is more important than a low ping, is a consistent ping. Playing a mage is all about timing and as long as your ping is consistent you can learn to compensate for a certain amount of latency, but if your ping is jumping all over the place it is very hard to do that.
It also depends on the template you are playing. Mage templates are a lot more sensitive to latency due to the necessity to precisely time spells than dexxer or archer templates are. Although with dexxers it can be very hard to close with your opponent if you are experiencing high latency.
It's hard to give exact numbers, but as a ball park figure, and there are many who would probably disagree with me, for the classic client I'd say a ping of 60 is probably the upper limit if you really want to be in the upper echelon of pvp'rs, especially as a mage. For the enhanced client you could probably be very competitive with a ping as high as 120.
As far as a lower limit, a lower ping is always better, so there really is no point below which there is no further advantage gained, other than 0.