corn mashing yield and calculator help please

[haeffnkr]

Hi,
I have been reading about ceral mashes w/ corn and I am confused.

Usually you add some water * gallon/pound ) with well cracked corn (or other adjunct ) and 10% malted barley- hold the temp at around 150-160 depending on which chart you find for 20 mins
Then ramp up to 200 or even boil for 30 mins.
Cool back to 148 to mash in with the wheat/barley/grains for about an hour
Cool to yeast pitch temps and pitch yeast.

Jimbos recipe says start at 200 and steep for hours then cool and mash?
What does happens if you miss the gelatin stage at 150 before the 200 plus steep/boil?
viewtopic.php?f=96&t=48126

Secondly -
Where is a calculator that tells me what my SG should be if I use X pounds of raw corn to 15 gallons of water?
I am trying to figure out what my SG will be with raw corn and malted grain.
I assume my SG target should be around 6 for most whisky type mashes.

thanks in advance
haeffnkr