Adding GeistGeld to the mix doesn't seem to be a big problem as far as I can tell. I have been doing it a while now and it seems to work fine for me with p2pool. However I am only running one 5870 card, maybe its worse when you have more hashing power?
Either you think you're mining GG but you're not, or GG is a totally screwed blockchain.
Let's assume for a moment that you are the only one in the world mining GG.
With 350 MH/s of a 5870 (having taken into account a large stales percentage) you should be solving a difficulty=1 block (2^32 hashes) every 12.2 seconds. Being that expected block generation interval is 15 seconds and retargeting is every 16 blocks, in a few minutes after you start mining with that 5870, difficulty should adjust to about 1.23 (give or take variance) and stay there as long as you keep on mining.
However, every time I looked at it lately, GG difficulty is from 0.06 to 0.12, which means that the average hashpower mining it is 20-40 MH/s altogether.
To prove my point, I did mine GG with a 5870 about a month ago, just for fun, and the difficulty adjusted within a few retargets from 0.06 to 1.3-1.6. When I stopped, it went back to 0.06. Strangely enough, I was getting only about 70% of the blocks , which means someone else was getting the other 30% which would be impossible if they were mining with only 20-40 MH/s as the previous difficulty as suggesting.
So, I guess something is wrong either with your claims, or with your calculations, or with the blockchain algo itself.