I'm really having a hankering for a Grafmatic, but they are expensive. Rather, I'm poor, because you can get them for under $100. But anyway, you can get 4x5 'bag mag's cheaper on eBay. Do they work ok? Do they work with a Pacemaker speed grapic? In what way are they different than grafmatics? I've been shooting action at the skatepark and even with a carpenter's tool belt to hold my film holders it's really cumbersome.

The bag mag will only work on a Graphic with a Graflex back. There is a clear explanation of the different Graphic backs (with photographs) on Jo Lommen's press-camera site,
http://www.xs4all.nl/~lommen9/
There were 3 kinds of backs on the Graphic cameras, which is confusing. The Grafmatic holders, along with most rollfilm holders, fit only the Graflok back. Some of the (earlier) Pacemakers were equipped with a Graflex back. Most had the Graphic (spring) back. The later (post 1950 or -51) were equipped with the Graflok back, which takes the more common rollfilm backs and Grafmatics.

Mine has the graflock back after all. O well, guess I need to save up.

Grafmatics also fit the Pacemakers with spring backs. A Graflok back is not needed for these models. It will slip in like a regular film holder. To use a Gafmatic on the older Anniversary models, which have less spring travel, you have to shim the springs out with washers. Some might be able to jam a Grafmatic into one of those, but it stretches the springs beyond their max.

The three types of backs are covered on this site as well:
http://graflex.org/speed-graphic/features.html#GraflokBack

The Bag Magazine was designed for use on the Graflex Back which is the only back available on Graflex SLR's. A Graflex back was made available for the Pacemaker so that Graflex SLR users that also had Speed or Crown Graphic could use the same film holders on both cameras.The Graflex film holders are wider than the Graphic/Graflok counter parts. There may be a different film plane register requiring infinity stops to be reset on a Graphic camera switched to a Graflex back. A ground glass pannel is optional for thr Graflex back.