The only R5s I have any first hand experience of didn't turn into bonfires although the GTT me & a mate caught in a car park had made a valiant effort to do so... It was parked up with steam & all gurgling hell spitting forth from the pressure cap & was just about to have cold water poured into it's overheated engine. (guess it had a bad BHG but at least they took part of our advice and boiled a few kettles worth to top it back up, whether it saved the engine or not I don't know, I'm sure they were adamant about driving home)
The other one never got near burning, the battery wouldn't have had the oomph to light a bit of wire wool & the brakes leaked all their fluid before the engine had a chance to get in on the act & overheat...
That said, an R5 (even a sporty one) is still on my bucket list to own, as are a 25, 21, Fuego and Vel Satis