6 months is all I have, what would be your method to finish your dissertation?
If you already have a first draft, then I think you need to have an honest conversation with Prof. X. The primary question needs to be "given what I have right now, is it actually possible to finish in 6 months? If so what are the crucial things that have to get done in order to pass the defense?" 

The best case scenario here is for Prof. X to respond to you with a list of specific, targeted issues that need to be fixed and a rough idea of which are the most important. 

If you can get that list of items to fix, then it comes down to prioritizing. If you can fix everything that simply must be fixed in 6 months, then I'd say maybe it's worth going for it. If you can fix all that in 4 months, and then fix medium to minor stuff for a month and revise for a month, all the better. 

On the other hand, if Prof X comes back and says, "Well I think you need more experiments," or "the results don't look significant enough yet" or "it isn't clear yet what all the issues might be" or something like that, then you're project probably simply isn't well enough defined yet to be able to be defensible in 6 months.

That said, don't underestimate how much can be accomplished in 6 months, if you're focused, well-prepared and willing to work long hours. You just need an expert opinion from somebody familiar with your work that obviously we're not going to be able to give you here. 

Best luck!