#2
I was thinking about doing this, seems one thing guys do is look for long scale guitar strings, then cut the ball off a old bass string and use that. Seems alot of guys was going with something around a 32-36 so Id say anything under 40. Dont hold me to that though.
Current Gear
Ibanez AGB200
Epiphone ET-280(with Dean Hillsboro Single guts and pup)
Epiphone EB-0

Gallien Krueger 700RB-II
Gallien Krueger 410 MBE
MXR Fuzz Deluxe
MXR Analog Chorus
Dunlop CryBaby 105Q
Boss TU-2
#4
From what I read, the .42 breaking point will be reached before you reach your desired tuning.
Current Gear
Ibanez AGB200
Epiphone ET-280(with Dean Hillsboro Single guts and pup)
Epiphone EB-0

Gallien Krueger 700RB-II
Gallien Krueger 410 MBE
MXR Fuzz Deluxe
MXR Analog Chorus
Dunlop CryBaby 105Q
Boss TU-2
#6
Id go with a .35 and hope for the best. Again Im not a expert I was thinking about doing this but never did. I talked to 2 of the most respected set up men in my area and hours of research on my own. Sometimes I know if you just try it, it works even though the masses say it wont.
Current Gear
Ibanez AGB200
Epiphone ET-280(with Dean Hillsboro Single guts and pup)
Epiphone EB-0

Gallien Krueger 700RB-II
Gallien Krueger 410 MBE
MXR Fuzz Deluxe
MXR Analog Chorus
Dunlop CryBaby 105Q
Boss TU-2
#7
I use a .32 and it's nice and light, a .35 should be fine. .40 would be pushing it
#8
Remember, you're going to have to balance the string gauges throughout all six strings. If you don't, your "C" string is going to come across much louder than the others. So if you increase the gauge of the "C" string, then you'll have to increase the gauge of the others. That's going to put a hell of a strain on the neck. I wouldn't use anything in the .40s for a high "C" string.

If you are dead set on using a heavier "C" string, you may have to go with a reinforced neck; or maybe a graphite neck. Either would be an expensive proposition.
"Maybe this world is another planet's hell?" - Aldous Huxley