Barb,
May I offer a suggestion for a fantastic High Mag Galaxy EP.
It is the Takahashi 7.5mm ED LE.
This particular EP has an 'ED' lense and gives incredible contrast and crisp image! In the GS 12" Dob at such a high mag it was amazing to see detail in NGC 4945 for the first time. This was after testing many different EP's at our astronomy Camps.
The 'LE' means long eye releif and it proved to be true. It was a very comfortable EP to use giving zero eye strain on the 3 of us that tested it in the 12".
12" at f5 is not an easy scope to get high mag detail. They are better known for their wider fields with EP's around 9mm and up to about 32mm. It is only when you get to your higher quality and price EP's that such crisp detail and amazing contrast is evident, and the Tak 7.5mm has proven to be the best tested in the GS 12" on this testing occasion.
Below I have attached a composite example showing exactly what we observed in March 2006 here in dark skies using the Tak 7.5mm ED LE with 10/10 Transparency and 8-9/10 seeing. The composite shows exactly the way I saw NGC 4945. I made sure I made it looks exactly the way I saw it. I cannot speak as to the quality observed by Darren and Peter but both were more than amazed at the quality of the Tak in the 12".
(I sound like a Tak salesman) 