The other thread established that it wasn't a pH issue, you're well within D47 alcohol limits, and now higher temps don't help either, which all points towards a nutrient deficiency.
Testing for YAN (Yeast Available Nitrogen) would give a definite answer, and isn't too hard, but probably not worth your time or money unless you're a commercial operation. Here's some simple directions if you want to go the scientific route: http://www.apps.fst.vt.edu/extension/enology/downloads/FermNitro.pdf
Using a champagne yeast will probably finish the fermentation, but if the nutrient deficit is big enough, then it too may get stuck. Alternatively, as WilliamSlayer mentioned, just add some nutrient and maybe re-pitch some more yeast along with it. I like to use a blend of organic and inorganic nitrogen.