Wrote 5 different versions of the parser. StlParserIndex2 has the best performance vs memory allocation in my testing. StlParserRegex is by far the fastest but also uses the most memory due to throwing everything into a string builder.

My testing results, in milliseconds, using the should model from this project: http://www.thingiverse.com/thing:38159
I tested other models but the results where similar. Regex was the fastest in all test cases, the two index based parsers where the 2nd fastest in all cases.

StlParser
2396
2352
2329

StlParserIndex
1680
1733
1691

StlParserIndex2
1688
1655
1716

StlParserRegex
1420
1450
1465

StlParserTokens
1776
1887
1889