It's hard to know but it doesn't sound like you went wrong. You mention "near vertical climbs" which doesn't sound like Sinister Gully. There is a gully just right of Sinister which is also a popular route on to the ridge. It's steeper, but shorter:
<a href="http://www.flickr.com/photos/mikepeacock/102126505/" title="And Steepens by Mike Peacock2005, on Flickr"></a><a href="http://www.flickr.com/photos/mikepeacock/102126505/" title="And Steepens by Mike Peacock2005, on Flickr">
</a><a href="http://www.flickr.com/photos/mikepeacock/102126505/" title="And Steepens by Mike Peacock2005, on Flickr"></a>
For what it's worth, Bristly is at the top end of grade 1, and is a step up from Tryfan North Ridge as it is more committing. However, the hardest/most intimidating part (I think) is getting up the gully. Once on the ridge I find things ease a bit.
Edited: 19/04/2012 at 20:27