The real impact of procs

I fail to realise what is the real impact of procs on overall DPS.

1- Is a proc (what proc? Purple?) better than a damage enhencement?
Does it depends on what attack it is slotted?

2- If not, how gimped is my attack if I only use 5 slots and no proc or if I build around global bonuses and save slots?

3- Are -res proc better than damage procs? Are Psy procs better than Lethal procs? Why?

It's hard to answer any of your questions in a nutshell. There's many parameters to consider, activation time, damage, recharge and even attack chain.

I look at it this way: determine the average boost I get from a proc, and from that look at each attack to see what is best.

A normal proc has a 20% chance to do 71 damage. That's an average of 14 damage per use.

A purple proc has a 33% chance to do 105 damage. That's an average of 35 damage per use.

So, a damage enhancement being 33% (if we work before values hit ED), a normal proc is going to be better than a damage enhancement as soon as an attack deals less than 14/0.33 = 42 base damage. A purple proc is going to be better than a damage enhancement as soon as an attack deals less than 35/0.33 = 105 base damage.

This is all going to change very soon with I24, getting more complicated if you want to minmax, but at the same time more smooth and intuitive for casual use, faster recharging and activating attacks not being the unequivocally best option anymore.

-res procs tend to shine in long fights against a single target. The more DPS you have, the bigger the boost you get from these becomes. Whether they're better or not than a damage proc will vary based on that, but generally speaking and in the specific scenarion of a tough ST fight, a -res proc is almost always better than a regular damage proc, and as your DPS gets to a certain point (think 150 or above), starts pulling ahead of a purple proc.

In AoEs, -res procs tend to be worse than damage procs, simply because minions and lieutenants die so fast you don't get to use much of the effect. Werner had posted an analysis about it at some point.

Regarding psy vs lethal, you'd have to consider average mob resistances (or perhaps more importantly but even harder to quantify, average mob resistances weighted for your own playstyle). It seems an awful lot of work for a minor difference so personally, I'm of the opinion it's not worth thinking about. I tend to pick psy over lethal given the choice, as lethal resistance is much more common in AVs than psy res, and AVs are the kind of target against which I care about procs being as efficient as possible.

Damage procs can be good, but nowhere near good enough that you'll be gimped if you don't use them. How good they are does depend heavily on the attack they're slotted in. For the current flat-chance procs, that just means putting it in a power you use frequently; when all procs become PPM next issue it will depend more on the specifics of the power and your attack chain.

Generally, I don't find it worthwhile to slot procs instead of enhancement values - procs are for any slots you may have left over after getting sufficient enhancement for acc/dam/end/rech. On the other hand, if you're slotting 5 pieces of a set, and it comes down to an acc/dam versus a damage proc, the proc usually wins because the damage is already ED-capped and the rest of the set probably provides enough accuracy.

If I ever have a choice between two damage procs that are the same except for damage type, like your lethal vs psi example, it doesn't hugely matter which you choose, but if possible I prefer to hedge my bets and choose a damage type I don't already deal. A Dual Blades character already deals all lethal damage, so a psi proc will be more helpful against enemies that resist lethal heavily, but I probably won't much notice or care when the proc is reduced against psi-resistant enemies.

Does anyone have a link they can share that tells about how all procs will work with I24? That is if there is one yet. If there isn't are they changing the way the numina, miracle and performance shifter procs work?

Thanks!

Maybe action speaks louder than words. Previous average pylon times was around 2:30 for about 380 DPS. I24 Beta using the same attack chain; same incarnate powers but slight change to build for 1:30ish for 550ish DPS mostly due to the proc changes. Around 170 DPS increase:

http://www.youtube.com/watch?v=i-eW_P_NqMg

Blow it up full screen and read the damage inflicted window. The final line at the end of each attack will indicate whether the proc activated by saying the word 'bonus' in the sentence.