I'm looking at the 300p or the 400p. I don't see much of a difference in performance stats on Viair's website. I'm leaning toward the 400p, but if the 300p isn't much different, then why waste money for the higher number? BTW, my nearly 10 year old cheapo Slime bit the dust.. It just wouldn't pump any more than 26 lbs and took nearly 10 minutes per tire to get that..... 2 hours to pump up, then paid 75 cents x 2 to finish airing up at a gas station.... any thoughts?