Hi Karen,
O.K., I will do my best to answer your questions. I will probably tell you more than you wanted to know, though, so be forewarned.
A single Invacare (in good working order, putting out good purity) is great for a Bobcat if you want to make small soft glass beads and small boro (slowly). But, if you want to make things that are, oh, say an inch or more in diameter, then you are going to want some more oxygen.
Adding a second concentrator that puts out similar psi (within 2 psi, any difference greater than that and you won't get very much out of the lower psi unit) would get a lot more out of a Bobcat. But, there are drawbacks to running two machines together. Besides the space concerns, you would have twice the noise, use up twice the electricity, and have two machines to maintain instead of one. If none of those are a problem, then going with two machines is a good option. If those things are a problem, then going with a single 10 LPM Regalia is a very good option. Keep in mind that a single 10 LPM Regalia will put out a true 10 LPM, while two 5 LPM machines will not put out a full 10 LPM when combined. They will backpressure each other slightly and you would get about 9 to 9.5 LPM. On a small bead torch, that difference is not a lot because that's more than most of those torches need for their biggest neutral flame. But on a larger torch, the difference is significant since they need much more.
The Regalia is not overkill for the Bobcat. It powers it very well and if you ever upgrade to a Lynx, you will have a good match-up, as well. I have run the Regalia on several torches and measured the flame outputs. For the bead torches (Minor, Bobat, Mini CC, Piranha, etc.), the Regalia powers them to full capacity or very close to it. For larger torches that require a lot more oxygen to feed them (like the Barracuda, Phantom, Bullet, etc.), you can get the nice wide flame that those torches offer and can work soft glass and some boro with a soft heat, but you won't be getting the hard driving heat that more oxygen would provide. That's to be expected, since most of those torches need about 20 LPM or more to get their full capacity and the Regalia only puts out 10 LPM.
Now, here's where it gets interesting... it all depends on how you work. If you work mostly on the centerfire and then use the outfire for short blasts, you have another option. The centerfires of those torches are the same thing as the stand-alone bead torches in their lines - the centerfire of the Phantom is the Lynx, the centerfire of the Barracuda is the same as the Piranha, etc. - so, you can run the centerfires off of the Regalia with no problem. You could add a holding tank and let it fill before you start or just run your torch and whatever is not being used by the centerfire can go into that tank. Whenever you need to kick on the outerfire, you would have a reserve of oxygen to do that. The larger the tank, the longer you can run the outerfire.
If you don't use the outerfire full blast, but use it a lot and mostly for a nice hot wide flame, then you could run two Regalias together or run the centerfire on a single Regalia and the outerfire on tanked oxygen. I run my Phantom of a Regalia and an Integra10 (the old version of the Regalia).
When running the center on the Regalia and the outer on tanked oxygen, you could run the outfire full blast whenever you wanted to and for as long as you wanted to - until the tank ran out.
The new Bobcats do have a tighter flame than the older ones, but they are still not as tight as the Cricket or the Lynx, as far as I know. The old cannot be modified.
The Bobcat and the Lynx use similar volumes of oxygen. The Lynx just uses it more efficiently and gets more heat out of it. The key is that third knob. That knob (the blue one on the top) controls the tiny injector tubes that lie within the fuel tubes. On a standard mix, you have a jet of fuel surrounded by oxygen. On the Triple Mix torches (Lynx, Cheetah, etc.), the oxygen is diverted into two paths - the main oxygen that surrounds the fuel, and a stream of oxygen that is injected into the middle of the fuel jet. This allows the fuel to be combusted from the inside as well as the outside and makes it burn more completely (this gives you more heat and is a lot cleaner). You are not necessarily using more oxygen to do this. You are just redirecting the flow. You can, of course, add more oxygen to the process if you wanted to to get a better oxidizing flame than you could with a standard mix.
When the blue valve is turned on, it also draws the radiant heat into the beam of the flame. This gives you a very hot, very focused flame. You can control how focused the beam is and how much radiant heat you have by how you balance the blue valve and the green valve (main oxygen). The more blue valve (injector oxygen) you use and the less green valve, the tighter the flame. By using the red valve (fuel) and the blue valve (injector oxygen) only, you can get a very hot tight flame. You can get that flame down to the size of a toothpick for tight spots.
When you use just the red and green valves, it's just like a standard mix torch and you can get a bushy flame with a lot of radiant heat. It's always a good idea to keep the blue valve at least cracked open, though. That way, there's no dead space around those little injector tubes. There are circumstances where you can turn off the blue valve, but you have to be careful or you can carbon your torch.
Kbinkster! I've got a battery of questions on oxycons and the Bobcat
. In a way, that's good. It means my Bobcat is great 
