Helios 1: During the first perihelion in late February 1975, the spacecraft came closer to the Sun than any spacecraft had before. The temperature of some components reached more than 100 °C, while the solar panels reached 127 °C, without affecting probe operations. read more
But for solar system travel they seem to be very promising, and NASA stated that they could reach 90Km/s. To give and idea voyager that is now reaching heliopause, the limits (arguably) of our solar system after 40 years, travels at 17Km/s, these ships could reach our fastest probe that was launched more than 40 years ago in 10 years if they left now. read more