i've seen some recipes that call for thicker mashes(1-1.25 qt/#) i do 1.5 qt/#, my question is how does this effect extraction? and do you just add more sparge water to get your target preboil?

Dude, I've come to the conclusion that the ratio makes little to no difference. I go for a thin mash (1.5qt/#) anymore just cause its easier to deal with.

Like you said get your target preboil wort right.

Check out Kai Troester's episode on basic brewing radio. It doesn't make much difference but within reason a thinner mash is the most efficient. He details all of this and gives exact numbers. I remember 2 qt. per pound being the most efficient but that is very thin.

In general though I would just use what works best for your system. If you have breezy brew days and want to manipulate something then that's maybe worth exploring. There are so many other things to explore too so it's your call.

I have found that thickness really alters your ph levels you need to find what amounts and ratio you need to hit your target ph. I shoot for a ph of 5.4 with my brews and hit it at 1.15 qts per pound but depending on the mineral levels in your water you may need more or less..

I seem to remeber something about enzymes and some working better in thick mashes with others working better in thin ones. I think it was similar to mashing at 155 or 145 but I forget what effects each were supposed to have. will re-reply if I find that info.

I have been using somewhere between 1.4 and 1.6 qts/gal as I remember reading a post by DC some time back that he almost always (at the time anyway) was using about 1.6 qt/gal. I typically takes my grist weight and plug into brew calcs to get sparge water volume, by adjusting the qt/gal ratio between 1.45 and 1.6 I am able to get it worked out so that I can lauter to the nearest 1/2 gallon, once I have determined how much sparge water is needed, I will add the required amount. Occasionally, depending if the OG of a 10 gal is over 1.075 I have to sparge twice simply to get enough wort b/c of mash tun size limitations. Currently using a 48qt rectangular cooler but moving to 70qt extreme cube in the near future.
This probably isnt the best procedure, but I have been hitting between 75 and 82 % efficiency.
And it tastes good, to me anyway...

From Kai's website....

"water/grist ratio – With today’s well modified malts, the mash thickness has little impact on the fermentability of the produced wort [Narziss, 2005]. This was also shown in the Limit of attenuation experiment. "

Full text at http://braukaiser.com/wiki/index.php?title=The_Theory_of_Mashing

From my brewery:

"Hey, the ratio makes little to no difference"

If you want the full story come buy you can see for yourself