In reply to Mr Boulder: The person I quoted is admittedly rather biased being a Malham local with numerous FAs there.
There are certainly some worthwhile grade 6 routes in the Peak, it is just that in general they are nothing spectacular compared, on a national basis, to the best routes on Portland or various other UK venues. Also, relative to how amazing the trad and bouldering in the Peak are, the lower grade sport routes are decidedly mediocre.
Mason Lees Quarry is probably one of the best mid-grade venues and a several of the routes there are excellent (when dry).
The main wall at Horseshoe is ok. At least, better than other parts of the quarry.
I also remember some fairly ok routes at Blackwell Halt in Upper Cheedale.
Provided you don't expect stunning climbing on every route, there are decent routes scattered around. It is really more a question of how much your expectations have been raised by climbing much better sport routes abroad or elsewhere in the UK.