Urgent help needed - large sarcoma in thigh

My girlfriend finally went to have an MRI of a very large lump in her thigh that has been there for 15 years. It is VERY large (about 6 inches). The MRI suggested sarcoma. We went to two orthopedic oncology surgeons at the top of their fields and head of their departments: John Abraham at the Rothman Institute of Jefferson Hospital in Philadelphia AND Richard Lackman at Cooper University Hospital in New Jersey which just merged with MD Anderson. 

Dr. Abraham did a CT assisted biopsy taking only about five very tiny strands of tissue in one area of this massive lump. The findings were as follows:

"The differential diagnosis includes a low grade fibrous neoplasm or perhaps a low grade fibromyxoid neoplasm. The degree of myxoid change is minimal. The quantity of tissue limits a definitive interpretation since such lesions often show considerably regional variability. Recommend complete excision of the lesion. Microscopic Description: The lesion consists of bland spindled cells that resemble fibroblasts. Immunochemistry for S100, actin, and cd34 are negative in lesional cells. Beta-Catenin shows only cytoplasmic immunoreactivity. Vimentin is, in contrast, strongly positive. Ki-67 marks very rare cells."

Dr. Abraham said that this biopsy did not indicate sarcoma exactly but did indicate abnormal, low grade cells they could not identify with such a small specimen. Dr Lackman said that he thinks it is indeed sarcoma but the sample was not big enough to determine.

Dr Abraham would like to proceed by going in with a very large incision and taking out both the lump and a margin of muscle "just incase".

Dr Lackman would like to do a smaller incision, take a chunk out, and while she is still asleep, look at it under a microscope. Then, if it is cancer he will sew up the incision, leaving the lump, then proceed with radiation and take out the lump after rounds of radiation are done. If it is not cancer he would just remove the lump without taking muscle margin. (I am pretty sure he did not want to take muscle margin even if it is cancer, and said there is only a 7 percent recur rate and this is a low grade....this seems to be opposite everything we have read)

We have an incisional biopsy set up for this Thursday at which point they will either sew up or remove.....but we do not know if that is the best way to proceed. We read a lot about recurrence. Are the recurrences mainly in high grade tumors? Does the size of the tumor determine the grade as well? Is there any benefit to an incisional biopsy and radiation before removal of the mass? It seems most people just get the mass out right off the bat. Is size an issue? I could really use a lot of answers here from people who know about this stuff. How should we proceed? Should we go ahead with the incisional biopsy and possible radiation?