I have some pretty extensive experience here so listen carefully. I have had 2 XP100s and numerous TC Contenders, and an MOA Maximum. Both my XP's were custome built. If you are really serious about building an XP I highly suggest you contact Apache308 through a PM. He has never built one that wasn't a hammer, and he has built them from 17 Fireball to 376Steyr. He IS the XP guru.
I am was a long time member on Specialty Pistols and still am but do not have a premium membership any longer. Over there you will be lauded with how to build a Savage Striker into teh best thing since sliced bread. People who are serious about handgun hunting and competition(silhouette) do not own Strikers.
The XP does have special linkage to accomodate mid grip stocks but plenty of folks have stripped the linkage and placed them in rear grip stocks. They take regular Remington 700 triggers after the linkage is stripped. The XP100R is also in the same class with teh plain old XP. It was a repeater and based on the model 7 action. It was only available in rear grip. The XP I still have was built on an XP100R action. It is of course rear grip, I converted it to single shot, and it is chambered for 223 with a fast twist and throated for80gr SMKs and AMaxs. The other XP I had was in 6BR and I converted it to rear grip(some people like reargrip some like midgrip). This was my dedicated US(unlimited standing)rig.
Good choices for an XP build would be 223 fast twist, 6BR,6.5CM,308, and a host of other wildcats and standard short action cartridges. Talk to Apache, he will tell you what you need to know.