Tara:
I could have probably gotten away ordering the regular size but ordered the larger one. I have a Yukon and my husband's vehicle is a fullsize GMC truck so -- the larger size should fit fine between the seats.
There really isn't much difference between the two sizes:
Regular: 15.25 x 8.5 x 6.25
Oversized: 19 x 12 x 7
The length definitely was NOT an issue even considering both Carter and Cooper in there together. The height difference isn't enough to be considered. 3 1/2" more width is probably a good thing for two dogs. If I only had one dog . . . I would have gone with the regular size regardless of the weight recommendation.
Lisa