Thanks for all the help guys.
I ended up remembering I had an old drill laying around with the old NICD battery packs. So I opened it up and it had some 1300 mAH sub c nicd cells. So i decided to take it apart and solder together 5 cells to stick with stock voltage. On my rapid strike I wired in a connector and man that thing rips. Off the charger the battery is 6.6v or so and it doesn't slow down at all even when emptying a 30rd drum. Sometimes it jams and just will pull through which is not so good but doesn't slow flywheels at all really. I am really happy. It works well. I also tried it in my stock infinius by removing the batteries and putting some adapters from D to AA in there that I soldered on some leads on the internal posts so the battery converters went in place of batteries and had leads so I could hook the pack up. This was all stock and it made a decent improvement. This is what I was looking for it doesn't have the shoot down that normally happens on full auto. Thanks for all the help. These are not as crazy as the other builds but for my situation it works awesome. And the battery pack seems to have fair life. I have fired 4 30rd drums, 10-18 round mags and still going strong. Now to find a good 6v charger which I talked with a local hobby RC store and they said they have one that works with lipo, nimh, nicd and multiple voltages so would allow me to buy one charger and if I upgrade down the road it will work for that and anything else I get.
EDIT: Last night I still thought the gun fired a bit hard for inside after some more testing and decided to try dropping a cell to 4 cells. Put me a little over 5v fresh off charer. Tried that and blasters fire good, fire a small amount harder than stock. Does bog some on the infinus that is all stock inside in long full auto bursts but doesn't shoot down near as bad. Found a sweet charger that charges to my voltage and any kind of battery and will cycle discharge. So thinking I am going to go with this route. Plus the 4 cell packs fit in stock battery slots and I am going to make some simple connections so I can swap between regular alkalines or these rechargeable packs that are homemade. I think better/larger and newer cells might reduce shoot down and also removing maybe the PTC on the infinus might help but that beast don't want to tear into since it is so complicated. My rapidstrike doesn't fire down just fires a little harder than stock, which no chrono but just from shooting it is a small improvement but not too much. I may post some pics if I ever get the cool battery trays done.