There are a few little things that worry me about your post.
First of all, we don't recommend using spermicidal condoms. They can irritate tissues and make STI/STD transmission more likely. There's not enough spermicide on a condom to be of any help, anyway, so it's a lose-lose situation.
(Also, remember that even if a condom is "lubricated," you will still need to use extra condom-safe lubricant, both to prevent the condom from breaking and for comfort.)
Remember that it is necessary to hold the condom at the base of the penis when withdrawing from penetration, to prevent it from leaking or from slipping off.
All this said, it sounds like what you've got here is a case of ill-fitting condoms. The brands are all cut differently, and it's worth it to buy a variety and experiment to find what fits you best and what feels the best to you.
Part of proper condom usage is proper fit. When you say "there's just a couple inches of slack at the end," do you mean at the head of the penis or at the base? There should be a bit of space at the head, when you pinch the condom there as you unroll it, to leave room for any ejaculate.
See this link for more: A Simple Condom Primer
"And when the answer that you want/Is in the question that you state/Come what may..." - Coheed and Cambria, "Blood Red Summer"