I've been playing with 4 PPC, 4 ERPPC, and 2 ERPPC/Gauss Marauder 3R lately and the conclusion is:
4 LPL beat any of the above combos both in quick play and CW.
Keep in mind that is on a heavily quirked mech - both regular and ER PPCs get 50% bonus velocity and -10% heat, while LPLs get meager -5% heat only.
In a nutshell, my ideas to fix PPCs are mostly in-line with what people mentioned in previous posts:
Fix projectile size/hit detection
Bring down IS ERPPC heat to 14 and iterate from there, keep clan version at 15
Bump speed to 1400-1500m/s
Change clan ERPPC damage to 13/1/1, instead of 10/2.5/2.5
The reasoning behind all of these lies in the wall of text below.
- Hit registration - abysmal, even with the 1800m/s ERPPCs. Projectiles just sink into terrain, unless you aim several meters away. Makes it nearly impossible to hit mechs that fire over a hill or around a corner.
Solution here could be to reduce the projectile size (as mentioned a few times in this thread), but I feel a complete rework/recode of the visual is needed.
- Heat - PPCs are pretty manageable at 10 heat, ERPPCs are not - on heat neutral map with 18 DHS, you may fire a pair three times before overheating and then run around for like 15-20 sec to cool off. Mind you, this is with 13.5 heat ERPPCs because of quirks. Combined with the poor hit reg, this makes them inferior to lasers, where you can ride the heat scale almost indefinitely by firing one at a time.
Solution - ERPPC reduction to 14 heat might help a bit, although I doubt it would make much of a difference in the end. Still, better to iterate in small increments than bringing heat down by 2-3 points.
- Velocity and sync with Gauss - as hinted above, the config I tried is nearly perfectly synced - 1800m/s ERPPCs and 2000m/s gauss.
It doesn't work very well, to say the least - 35 PPFLD is not nearly as impressive in 2015, as it was before clans came out. What usually happens is you may fire a few shots, then an EBJ (insert random laser boat here) would take notice of you, get close, barf twice and move past your wreck. To be honest, this weapon combo only worked well because of poptarts back in the day, due to minimum exposure in mid-flight. Now you'll eat full laser durations nearly every time you fire.
On the other hand, 1800m/s ERPPCs feel damn nice - you can actually hit moving targets at long distances, as well as lights zapping around at 140+ kph.
Solution - bump speed to 1400-1500m/s. Maybe tone down some of the quirked mechs, but I wouldn't worry too much about those - most of them will remain pretty bad compared to the top dogs.
- Clan ERPPCs - my impressions are from a pop-tart Nova and 28 DHS Warhawk, both with 15% velocity quirk and TC2. They can work fairly well with cautious heat management, but the splash damage is meaningless and you basically get the same thing as the IS version, for less slots and weight.
Solution - keep heat at 15, change damage to 13/1/1 instead of 10/2.5/2.5, buff speed to 1400-1500m/s. Still worse than clan LPLs, but could at least be considered as an alternative.