When I was fishing a pond this summer with lots of low double carp that fought like anything in the margins on the waggler I had to step up to 8lb line and 7lb hooklength. Places like that are rare for me though as I fish places where low doubles are rare and I would usually think 8lb is a bit heavy for float fishing, going to 6lb maximum for summer fishing. In Winter you can get away with less. All depends on the venue (snaggy or not) and the size of the fish.
Forgot to add I go maxima brand wise, drennan floatfish decent as well.
Agree with PG that 6lb is too strong for 90% of float fishing, 3lb fine for most things and 4lb the sensible max. Would only use 6lb on the float if deliberately targeting double figure barbel and carp.
I use loads of different makes of line like drennan feeder or shimano aspire good lines but if I was honest Maxima or bayer I have most faith in ..6 to 8lb on feeder 4lb on pellet wag 3lb normal wagler you wont be far off with those lines . I try the others because they're newer and I try to get an edge but bayer and maxima are just as good if not better in my honest opinion