The XML will probably run at around 8-15k.  Hopefully that won't be a problem.

Select   t1.AccountNumber

                , t1.originalBilledAmount / t3.ProcRecords As AdjBilledAmt

                , t2.PatientPrimaryKey

                , PhysicianID

                , t2.cptcode

From  tbl_BillingMaster t1

Inner Join tbl_PerformedProcedure t2

  On  t1.PatientPrimaryKey = t2.PatientPrimaryKey

Inner Join

 (Select  t1.AccountNumber

   , Cast(Count(*) As decimal) As...