What are your power goals?
How fast do you want to get there?
What kind of budget are you on?
If you are looking for less than 200 HP the stock cams would be fine. You will be able to make more than that on them. They will favor low end and quick spool but you will feel them restricting the upper RPM pretty seriously.
Cams will really open up the upper RPM and allow you to get the most power out of it.
This would be my first cam recommendation.
http://www.matrixgarage.com/?q=products ... agte-4agzeIt would work very well with a turbo build and should sacrifice very little down low while gaining a good bit up top.
A little cheaper option would be the Tomei Poncam.
http://www.matrixgarage.com/?q=products ... 64-81mm-exThis is my most popular item in my store and everyone who buys them raves about them. They are aimed a little more for the NA builds but if you compare the specs to the above Kelford you will notice the specs are very similar.
How much boost can one run is one of those questions that's kind of meaningless. This will be effected by things like your cams, your tuning ability, monitoring equipment and knock prevention.
There are many people who have run over 20 PSI reliably. I have seen a couple threads and dynos on youtube claiming over 500 WHP on stock GZE internals.
You may find some info in here helpful.
http://www.matrixgarage.com/content/yos ... oing-4a-ge