have just come acrosss this thread, so sorry to but in!
I did this race as my first marathon last year (bought for me by my sister as a birthday present!), I managed 4hours 36, and did London last week in 3hours 57, so yes for us slower mere mortals about 30 mins extra on time is about right. Also with regard to your comment about parking, thet start and finish are in different places, but I presume there is a bus that takes runners from Llanberis, (we were dropped off by hubby) so don't know. Hill at 22 is a killer, so be prepared to walk a bit (or a lot!).
Atmosphere however is fantastic, not quite the amount of support as FLM but from other runners it's great, lots's of very friendly people, have entered again this year.