At the turf club in our area, the lap times on 17.5 are comparable with 13.5, not uncommon to see the classes mixed and for many 17.5 cars out pace some of the 13.5's.... even down the front straight!
Don't underestimate 40A cycling... the key is to use a discharge bank and dump the pack before you charge it, and timing is everything, you want to cycle it no more than 10 min before your race to get the best results. Lately they haven't been teching and I suspect a fair amount of cheating as well, I know as a fact that some drivers are charging to 4.35V/cell and not running blinky... even the faster 13.5's are on pace with many mod cars!
I've grown to appreciate Mod 4WD SCT and Mod 4WD Mini Truggy on the dirt track (the club hosts both dirt and turf at the same facility)... the Mod field is more level with way closer racing than the stock classes, go figure???