So for my band, I have recently decided to stick to my four string and drop tune to

B F# B E

the problem is is the strings are VERY loose and make some nasty noises.
so I'm going to buy heavier gauge strings to resolve the problem, but how much heavier of a gauge should i get? strings are 20 bucks a pack, and I don't have the cash to experiment.
Peavy Cirrus 5 string
Squire Jazz bass
Berhinger ultrabass head, 450 cabinet
Resident Marvel Comic expert of the Bass Militia, PM Dinkydaisy to join
]My band's myspace
Light 5 string bass set? May need to do some nut work.
Schecter Stiletto Studio 5
Ibanez SRX2EX1
Gallien Krueger 1001rbii
Gallien Krueger Neo 410