Question about LINQ // performance

In terms of performance, there's no difference at all between the two. They both boil down to exactly the same IL:

.method private hidebysig static bool  '<main>b__3'(class LinqIl.Article x) cil managed
{
  .custom instance void [mscorlib]System.Runtime.CompilerServices.CompilerGeneratedAttribute::.ctor() = ( 01 00 00 00 ) 
  // Code size       21 (0x15)
  .maxstack  2
  .locals init ([0] bool CS$1$0000)
  IL_0000:  ldarg.0
  IL_0001:  ldfld      string LinqIl.Article::StorageUnit
  IL_0006:  ldstr      "some unit"
  IL_000b:  call       bool [mscorlib]System.String::op_Equality(string,
                                                                 string)
  IL_0010:  stloc.0
  IL_0011:  br.s       IL_0013
  IL_0013:  ldloc.0
  IL_0014:  ret
} // end of method Program::'<main>b__3'</main></main>

If you want to prove this to yourself, all you need to do is run ildasm and disassemble your code.