Hi Guys,
13.5 Lipo is about 2-3 tenths quicker than 4-cell 17.5. That's with the Lipo car at 730 grams and the 4-cell at 865.
When we first started testing, it seemed like they were pretty even, but as we've tweaked on the Lipo cars (both electronically & chassis set-ups), they are definitely quicker than 17.5 4-cell now.