Heat tape/Power questions

What are the reasons to use the higher wattage 3'' heat tape? Faster heat up time?
I am building a rack and I'm not sure which one to get. I am tempted to go with the lower wattage to save in electricity.
Its a pretty big rack to heat, should I check into the 500 watt helix module or just get a 30 amp mercury contact relay with a 120v coil and use the helix to control? The relay is about 90 bucks, I not sure how much helix gets for their module.
Thanks for any help:confused:

The different size's of flexwatt primarily apply to the size/type of enclosure. For example:

I use the 4 in. (8 watts per foot) in my rack. I live in Houston, TX so I don't need to cover such a large area underneath to keep the temps where I need them. I would suspect that someone up north would use the 11 in. (20 watts per foot) to cover a larger surface due to the colder environment.

I'm no electrical engineer so I really can't say use the 3 in. over the 4 in. because of (insert answer here). What I can say is I just took demographics into account when I made my choice and have been happy since. Hope that helps a bit. :)

Helix or Herpstat. You can't go wrong with either.

Sorry for the misunderstanding. I am talking about 3 inch heat tape that is available in 6 or 10 watts per foot.

Oh, my bad. That's what I get for assuming. I won't be able to help you there, I've never used it.