increasing max_pred_locks_per_transaction, what shuold I look for?

Hi all,

I've got a situation where I need to increase max_pred_locks_per_transaction value to allow the addition of a slony
nodeto complete on postgres 9.1. We had this issue before and we increased the default value from 64 to 128, but now we
havea sync that takes even longer and the value for 128 isn't enough either. 

Looking at the activity I saw in pg_locks, I believe I need to set it to at least 256, but a value this high I want to
makesure that I don't cause other issues with the system. The docs mention that it may need to request more system v
sharedmemory, but should I also re-calculate other parameters such as work_mem, shared_buffers, etc? 

Current System:
Postgres 9.1.3
252 GB system memory
shared_buffers 40GB
work_mem 200MB
max_connections = 300
max_prepared_transactions = 0

free -g
             total       used       free     shared    buffers     cached
Mem:           252        239         12          0          1        221

I have a lot of cashed memory, but I just want to make sure this isn't something that cascades out of control and I'm
suddenlyhaving major 'out of memory' issues. 

thanks in advance,
- Brian F