Propagated yeast - Weaker by the batch

I've recently tried to make the transition from dry to liquid yeast and hoped to offset the cost increase by maintaining the yeast. I split the vial 75/25 into the first batch and a starter (dark DME and hop cones at ~1.05 with a 15 minute boil attempting to follow "How to Brew" by John Palmer) and saw rapid work and complete fermentation of a 10.5% ABV Belgian White. After the airlock was bubbling regularly, I stuck the yeast mix in our kitchen regrigerator.

Second batch was a 8.5% ABV stout and I poured 75% of my yeast mix into the fermentor and replaced the lost volume with the stour wort. Fermentation of the 5 gallon batch was slow and did not complete for roughly one week. I had already stuck the maintained yeast in the fridge when I saw consistent bubbling.

Third batch is inderway and a 5-6% porter following the same 75/25 with wort replacement of volume. Nothing twitched for the first 24 hours, so I became nervous. I added some yeast nutrient and energizer to my maintained yeast mixture. It is slowly bubbling now at about 40 hours, but the fermenter is at atmospheric pressure (no nutrients added). The third batch was also the first time that I've used a pump and airstone to aerate the wort immediately prior to yeast addition, which I thought would speed things up.

If you've stuck with me this long, then I'm hoping for some guidance on what I've done to my yeast starter. The yeast was a White Labs Dry Ale Yeast and I brew at roughly six week intervals.

How big are your starters?

http://www.mrmalty.com/calc/calc.html

I used a 40 oz bottle for the starter but left about 5 oz to prevent blow off.

I didn't want to let the main batch sit too long, so I reverted to a dry yeast that has shown early bubbling within 4 hours. The starter bottle now has a nice kraussen and the three piece bubbler is working at roughly 30 second intervals.

I would call the starter healthy, but it took roughly 36 - 40 hours to reach this point (plus a little yeast nutrient and energizer).