In reply to bobpilgrem:
Between the devil and the deep blue sea here mate! Choose either getting flamed for daring to abb off or getting flamed for being unable to extract yourself from a crag ant the MRT being called out! (due to lack of abb'ing skill maybe??)
Seriously, the local ethic is not to encourage abseiling at Tremadog but done properly it hasn't ever been a problem for me both climbing or abseiling. The best station IMO is at the top of Grim Wall. It usually has an assortment of tat in place but if you are planning this you have no excuse to buy a few meters of tat (11mm static) and a mailion. Do everyone a favor and cut away any old/suspect tat and install your own. Look carefully to see if anyone is on the routes below you - Grim Wall area is home to many fine routes and at the weekend, it'll be busy!
2 x 50m ropes reach the foot of the routes no problem so your 2 x 60m will be fine.
Abseiling is an essencal mountain skill and it should be practiced now and again. Done properly and with a little thought, it need not be a problem for anyone else at the crag or the crag enviroment in general.
Hope this helps.