More hashpower is never going to reduce the variance compared to other pools.  You may get more shares on p2pool with more hashpower, but you will also get more shares on the other pools with same amount of hashes.  So I imagine you would still complain about "variance" even if you had more hashpower.  Shares on p2pool are far more valuable than other pools.  So in the long term, all other things being equal, it should be a wash, luck playing a big part.  The p2pool difficulty is reflected in the time it takes to generate a p2pool block.  The target being 10 seconds I believe.  The only way to reduce difficulty is to reduce this target time of 10 seconds (or reduce the total hashpower in the pool).  Reducing target time would have other consequences that I'm not sure you would be pleased with.  The effects of latency are already high.  Reducing target time would magnify those, if I understand correctly.  The sensitivity to latencies maybe the underlying cause behind your earlier comment, "p2pool can not be reliably run on a home DSL connection".  Which is not true, at least from me.  Anyhoo, sounds to me like having a constant trickle of payout no matter how small, is important to you.  I would suggest BTCGiuld is the right place for your hashes.