So I've been meaning to do this for a while, and just haven't gotten around to it until now. I have an Ibanez ARZ307fm. It's a 25" scale 7 string tuned to B standard, and currently I'm stringing it with that Dunlop Heavy Core 7 set. That's .10-.48 with a .60 on the low B.
It's fine, if a little loose on most of the strings, but the low B in particular feels pretty flabby and has trouble staying in tune, so I think I need to go heavier. I was thinking about getting the D'addario 8 string set and just throwing out the .09, which would make it .11-.54 with a .65 on the bottom. That might be a bit of a jump though, so I was also thinking of putting a set somewhere in between on juststrings. Maybe like a .10-.54 with a .62 on bottom?
Ultimately I know I need to just try some stuff out and see what works, but I also know that there's a bit of a science to the whole string gauge vs scale length thing and I'm hoping some of you are more knowledgeable about it than I am. Any recommendations?
When i had a 7321 (so same scale & tuning & whatnot) I think I stuck with a DR 7 set, 10-whatever it was. I use a 27" Agile now but I tried that same dunlop heavy core set and left them on for all of about 2 days. They were OK in B standard but sucked in A standard. Right now I'm using an EB Cobalt Chrome set...they feel terrible when you first put them on but after a day or two they're pretty nice. They're pretty tight in B and just stiff enough in A, so might be perfect in B on your 25". If you try them, just remember not to judge too harshly until you've played them in for a good couple hours. Can't say I'll buy them again though...
tl;dr: I'm not much help :/