The .45 ACP and the .45 GAP are based on the same case -- .45 ACP -- but the GAP is shorter in length.  The GAP round is a "compact" version of the former designed for Glock pistols (GAP = Glock Automatic Pistol).  It supposedly has less recoil and lends itself to smaller pistols having a .45 punch for concealed carry.  I'd consider it a wildcat cartridge that would fill a special niche.  Myself, the .45 ACP works just fine and it is widely available.  The same may or may not be true of the .45 GAP (depending on where you live).  Wikipedia has a good write-up on the .45 GAP.  Do a search on .45 GAP.

 

The .50 GI (GI = Guncrafter Industries) is a modification of the .45 ACP case to take a .50 bullet.  The case is a rebated rimless case (that is, the base is smaller than the case diameter.  This would be the maximum bullet diameter consitent with federal law for a handgun.  The .50 GI uses a 275 grain bullet @ 875 fps vice 230 grain bullet a @ 875 fps for the .45 ACP.  You can find details on the www.guncrafterindustries.com site.  Likewise, Wikipedia has a write-up under .50 GI cartridge or .50 Guncrafter Industries cartridge.  The .50 GI is used in a modified M1911A1-type pistol.

Re: The ice storm didn't affect us much.  We got some, but the weather warmed up.  I suspect that the Chicago area may have gotten it worse due to the "lake effect."