Don't waste your money on the GP4300's. My IB 3800's are far better. I would stick with the IB cells. My 4300 pack feels flat. I have some really good GP 3300's that I run and just let my kids use the 4300.
Right now IB4200 are the favorite cell to use, has higher voltage, lower internal resistance. That why the Sanyo and GP seem flat when you've use either the IB3800 or IB4200. I haven't used the EP cells, so I can't compare them against the others.
IMO when the IB cells came out, 3600's they were good for runtime that was it, those were running against the gp3300's at that time that was the cells to have. now like any other company out there they went back and reworked there cell and came out with the 3800 cell which crushed the GP3300 cell, from there 4200's, then 4200shv and now 4200WC, from the problems IB had recently and not being able to get cells, venting or not even charging, matchers/racers had no choice but to try the EP cells again. there first batch IMO sucked, maybe a step above the gp3300 cell, I have tested/ran the MII ep 4200 pack and have to admit, they seem to be as equal if not a tad better than the IB pack. reasons being, they have the punch like the IB up front and are consistant, lots of voltage and runtime, never encountered venting, all cells while charging had close temps. you can run them 3times in a day of racing,HMMM that means you dont have to have so many packs in your box---more money in your pocket, what I did notice as a draw back like the IB cells is that you MUST put charge back in them, they self dis fast, LOW LOW IR's. you will see more and more people running I think, I havent received my new batch of IB's yet but also hear good things. probably going to be a mix of people running IB and EP saying one is better than the other. I trust what my matcher says and going to roll with that.
All I can say is be very very careful. I bought 6 new IB4200WC packs from a matcher back in Jan., and all I can say is they are terrible. I will not buy packs from them again. Run times are about 100 sec. off, Volts are pretty close but drop very quickly below 4.90V. You can tell it on the track. Avg lap times at my track for super spec are 6.2 - 6.4's. I get 2 laps max then drop off to 6.8 - 7.0 for the rest of the race. My old batts are not that bad! If you can get some IB4200's from a good batch and from a honest matcher they run great, but got to be careful. I would not buy IB4200 SHV, they just don't have the run time. I have 2 packs and are very strong but don't last long enough to run the gear that I need to run to be competitive.