If you trying to learn the ring I'd strongly advise against the Ruf yellowbird and Honda NSX ( the Ruf RGT is ok to use). There's nothing wrong with them once you know your way around the track but there not starter cars for the ring. It's alright saying the Ruf is unforgiving but that's exactly what you don't want as you'll get thrown off the circuit too many times and get frustrated. There are alot of complex camber changes and braking points in the Ring and the NSX is not much better, it's a twitchy car unless your start tuning the suspension to suit.
If you want a car that will let you focus on learning the track rather than having to concentrate on keeping the car from spinning then the easiest car would be a Nissan R35 GTR, if you want to stick to rwd then a BMW M3, M3 CSL or M3 GTR would be perfect.
To give you a benchmark we race in a 333hp per tonne forum so in the BMW M3's it's about 400hp and 1200kgs and I get round in 7min 15 seconds. The Skyline R35 GTR is quite a bit quicker and can lap in 7min 04 seconds, this is with 580 hp and 1740kgs. Both these are also set using sports soft tyres no TCS and ABS set to 1.
Also if you find the number of corners bemusing to learn and forget what's coming up next then break it down into learning different sections at a time. The reason I say this is it's a very high speed circuit for example after the first complex of left and right turns you go down the hill and up the other side approaching a right hander. The braking point for this is key as it's a double apex corner and go in too fast and you run off onto the grass and into the barriers, also after the straight that follows same thing again, you'll be doing circa 160mph braking into a fast left hander, get it right and you can carry alot of speed, get it wrong and you'll be off into the barriers.
The Ring is a narrow circuit so you have to be precise and know where to put the car for the next bend. I run about 10 laps of the Ring most nights and once you know where it all goes it'sa very challenging circuit and you'll see your times tumbling down.
Good luck and enjoy.