I have the GG&G, it's a big heavy powerful breaching hawk. It doesn't cut wood, it smashes it into pieces. It's 44oz, compared to most Winkler's 24oz. That extra weight has it's pros and cons. It's great to train with, to build strength and endurance. I feel slow with it, even with short jabs, a full on swing is brutal, unless you miss. The strength it takes to recover from that miss is also good training, but would be a mistake in a real fight.
For utility, I would prefer something that actually cuts wood, but I'm a backpacker, not SWAT or military, etc. For the vehicle, maybe the GG&G would be great, but it's so thick I can't imagine it even cutting through sheet metal. It would excel at going through glass, or a cinderblock wall, sheetrock, or anything that can be smashed.
I have the R&D, GG&G, a SOG Fasthawk, and a Winkler RnD and a Ranger Renegade on order. Actually, Justin mailed the Renegade today. It's a wooden handled forged spike hawk. All the reviews of this hawk are good, sure a wooden handle can break, but it's still very sturdy. I plan on using it on backpacking trips, to cut a bit of fire wood. I'll do some training with it for fighting, I might throw it some as well.
The Spax seems like a good breaching hawk. The rounded top spine and that curved spike would allow for serious leverage. It's not the thickest spike, but I've seen it act like a great can opener and pryer. But, with the RD Hawk, you have a pretty stout breaching hawk right there, not to mention the S&W E&E.
IF I were you, I'd look more towards the middle ground, less breaching. I think once you get that Winkler, you'll feel a big difference in mass distribution. So, you'll have a couple of thick(slow) breaching hawks, and then one pure fighting hawk. There are lighter faster hawks out there, just depends on what you want them to do. The offerings from RMJ Tactical, for example, are geared towards utility, and I bet they can handle a fight as well.
Smaller hawks are faster in hand, easy to conceal, the Jenny Wren for example, or Winklers Stealth Hawk. For less money, there's Coal Creek Forge, Steve has his hawks on that auction site sometimes.
IMO, the Winkler RnD is a fighting hawk, and excels at close quarters fighting, Sayoc style. At 13" long, they will carry better than longer traditional hawks. Yet, in the open, when fighting, I'd rather have a bit longer hawk. More reach, all the weight is at the head, the heads are usually longer(spike hawks), and the speed at the head can be faster, just depends on the weight and user strength. I'm just saying there's a different approach to fighting with a longer hawk. All these shorter tactical hawks have there place, and I love their style. Just don't discout a wooden handled hawk, they can be tough, deadly, chop wood or demo a house. Look at this review of the Renegade...
http://www.themartialist.com/1206/rangerrenegade.htm
Oh yeah, have you seen these? A high density polymer Winkler-Sayoc trainer...
http://www.bloodnbonesgear.com/id39.html or the aluminium ones...
http://sayoc.com/store/product_info.php?products_id=308&osCsid=248ed379630584d4dda84379a4a28c3d
I got myself a polymer one, I want to do some hands on training without hurting anyone, they are made very well.
