Why split it, if you worry about a pool going down you can just setup a backup server, so if one pool is down the miner will automatically switch to the backup pool and you will not loose anything. Try the latest poclbm, besides the performance improvement it also comes with a backup pool server option.
As for PPS, it depends on the current pool luck, if the pool is lucky (average blocks below difficulty) then Proportional is better, if the block size goes higher than the difficulty for a while you may be better with PPS. In general with big pools such as deepbit there is no need to go for PPS as their average long time luck is usually about the difficulty level, and blocks are being calculated quite fast, so not much need to risk it with PPS and the higher fee and constantly monitor if at the moment it is better to go for PPS or Proportional, so better stick with Prop.