I normally use M5B flashbulbs, but have used bigger ones. Basically whatever I can get my hands on.
The reason I mentioned it is that scrounging flashbulbs can sometimes get expensive. I have a couple hundred Sylvania Press 25s in my stash that I continually replenish and will occasionally pull out because I also like their look. That longer ramp up and down time to and from full intensity softens the edges of subjects. I like that closer-to-correct vintage look.
But at anywhere from $0.50 to $1.00 per bulb, sometimes I like to substitute an electronic flash instead. To that end, I recently purchased a brand new Sunpak 622 Super unit with a zoom head. This unit is rated by Sunpak at GN200 at ISO100, which is a near perfect match for the Press 25s. I verified this by setting up a flash meter outside after dark (no reflected light) and in actual use found the two to be virtually identical in light outputalbeit both somewhat less than GN200, as would be expected. So performance-wise it's a near one-to-one substitute for the bulbs I use.
The reason this is interesting is that someone somewhere seems to have gotten their hands on a large supply of NOS 622S units and zoom heads.* Presumably this is Sunpak finally emptying their warehouse of an obsolete (to them) product line. As a result, these units can at the moment be found all over the place for pennies on the original dollars. I paid USD $179 for a new unit with a new head. At one time these professional system flashes went for something like $600-800, I believe.
In fact, I actually jumped in for two units, and set one aside as a backup for down the road. I then cobbled together a nice looking and very robust mounting interface to my 4x5 Crown Graphic that uses the original Graflex Graflite clamps. The 622S is heavier than the Graflite, but also less bulky and less expensive to operate. Last time I looked B&H was still carrying these NOS units, as were several eBay vendors.
As you (and others here) also use a Graphic, I figured I'd pass the info along before this current supply of NOS 622Ss dries up, in case you hadn't heard and might be interested.
Ken
* So far I've only seen the zoom heads (ZH-1) advertised as new. But this was the most desired option back in the day.