What batteries to buy and why?

OK, I've been using Maxamps lipo packs for a few years now; but I've only just started using them in 1/8 scale conversions. When I first got my buggy converted, I ordered some of the 6Ah 4S2P packs, because they were rated at 120A constant. My setup is a 7XL with a Mamba Max Speed controller running 14/46 gearing. I think it's all setup right. Neither my motor or esc ever get to over 140 degrees or so.

The thing is that I've now killed three of these 6Ah packs. Just tonight, I puffed one and I wasn't doing anything nuts or off the wall. I was just running on a track. From what I understand, my setup might hit 120A in spikes, but that's about it. It appears that the Maxamps pack cannot deliver what they are rated for. Now, I was getting ready to order some of their 5Ah packs, but I'm very skeptical. I even considered going with an 8Ah pack, but my friend got one and although it hasn't gotten blazing hot, it's gotten to over 130 degrees, so it's obviously being stressed. I feel bad about that too, since I recommeded the maxamps pack to him.

At this point, I'm giving up on trying to find "bang for the buck" with my batteries. If I destroy the batteries trying to get them to do what they are supposed to, there isn't much bang for the buck.

Can anyone tell me what the absolute best battery pack that I can get is? I want it to be able to easily keep up with the demands of my system, but I also don't want it to be a brick. Is there actually a 4S pack with a capacity of 5Ah or so that can really deliver without toasting itself? I'd love to be able to find some that will fit my battery tray. Unfortunately I designed and built my whole battery setup around the maxamps packs.

Thanks.