M16 fitted with laser sight, scope, silencer, and M203 grenade launcher under the barrel. I would pack a couple smoke grenades for when I get to the evil scientist (I can become invisible!) By weight I would mostly carry clips of bullets rather than nades.
With a high quality sound suppressor, shooting doesn't have to attract the attention of a lot of zombies. With the time stipulation, the battery life on the laser sight isn't an issue. I'd still mostly fire in semi automatic mode rather than three round burst to minimize time spent reloading.
An uzi 9mm with fold-out stock or P90 might be better for close encounters, but my plan would be to avoid close encounters as much as possible, hence a quality assault rifle with all the options.
And when I catch that evil scientist, I'll kill him quickly, not out of mercy, but pragmatism. We know what happens when you stop to torture from the first Lethal Weapon movie and True Lies.
Aside: I just started my second time through resident evil 4, it's the first time in a long time that I've immediately wanted to replay a long game after finishing it. I sold my thermal scope to pay for the broken butterfly upgrades though, so I'll be using the shotgun to kill the first two regenerators again. It only takes about 10-17 shots depending on placement, speed, and firepower level. This time I sploited the chickens, I have two dozen eggs in my inventory. All you have to do is leave the area and come back and they lay again, you don't have to save and reset. Also, when I fought the cage match with the garrador the first time, after he killed me a dozen times in a row I retried again and instead of the garrador and a dude I only had to fight two dudes, which means I missed out on a 15k treasure drop but didn't have to keep dying.