try this (I think this is what you want..)

declare @x xml = '<row id="LD122487292000" xml:space="preserve">

<c1>USD</c1>

<c2>20120904</c2>

<c2 m="2">20120904</c2>

<c2 m="3">20121004</c2>

<c2 m="4">20121102</c2>

<c3>20120904</c3>

<c3 m="2">20120904</c3>

<c3 m="3">20121004</c3>

<c3 m="4">20121102</c3>

<c4>-250</c4>

<c4 m="2">150</c4>

<c4 m="3">95.18</c4>

<c4 m="4">-145.18</c4>

<c5 m="4" />

<c6>-250</c6>

<c6 m="2">-100</c6>

<c6 m="3">-4.82</c6>

<c6 m="4">-150</c6>

<c7 m="4" />

<c8 m="4" />

<c11>-12.47</c11>

<c13>0</c13>

<c15>0</c15>

<c51>20120904</c51>

<c52>20140904</c52>

<c53>-132</c53>

<c57>-250</c57>

<c57 m="2">-250</c57>

<c57 m="3">-250</c57>

<c58>-4.95</c58>

<c58 m="2">-5.5</c58>

<c58 m="3">-2.02</c58>

<c60>26.4</c60>

<c60 m="2">26.4</c60>

<c60 m="3">26.4</c60>

<c61 m="3" />

<c62>20120930</c62>

<c62 m="2">20121031</c62>

<c62 m="3">20121111</c62>

<c63>-4.9499999999998</c63>

<c63 m="2">-5.4999999999996</c63>

<c63 m="3">-2.0166666666665</c63>

<c68>0</c68>

<c80>20120904</c80>

<c162>0</c162>

<c170>20120904</c170>

<c172>4058.5</c172>

</row>'

declare @m INT

select @m = MAX(ISNULl(t.c.value('@m', 'int'), 0)) from @x.nodes('/row/c62') t(c)

Select t.c.value('./@id', 'nvarchar(100)'), t.c.value('(c1/text())[1]', 'NVARCHAR(10)'), t.c.value('(c58[@m=sql:variable("@m")]/text())[1]', 'nvarchar(10)'), t.c.value('(c62[@m=sql:variable("@m")]/text())[1]', 'nvarchar(10)') FROM @x.nodes('/row') t(c)