Mash Tun vs. regular PM method?

I'm trying to decide which method to use for my first Partial Mash. I was looking at the PM method that comes in the AHB directions and it is right along the lines of Deathbrewer's "How To" he posted here. With 3.25 lbs of grain it calls for 2.5 gallons of mash water and 1.5 quarts of sparge water.

Using the 2 gallon Rubbermaid Mash Tun I calculated 4 quarts of strike water for mash in, and 4 quarts of sparge water. (batch sparge)

It looks like I'm using less water in the mash tun method. Will the results be the same? Will the mash tun method result in higher SG due to the lower amount of water? I prefer to use the mini-mash tun because I want to practice toward going all-grain.

Is there anything I should be looking out for?
Considering I am going to top off up to 7 gallons for the boil, is there any problem with upping my sparge water (using the mash tun method) to get a bit more of the fermentables? Will it begin to give me crap I don't want?

I started out using a large past pot to mash in and put that in a warm oven (heated up, then turned off) for the mash. It worked fine, but after a while I picked up a 5 gallon beverage cooler and put a ball valve on it and I REALLY enjoy using it. It's so much easier than messing with the pot. I don't even use a manafold. I just get a big paint strainer bag, line the inside of the cooler with it and add my grain and water.

I think the end result will be the same. The grains will mash the same, but the cooler really makes it a piece of cake.

My 2 gallon cooler is converted with the ball valve and SS braid, but I'm trying to understand how the different volumes of water will affect the mash.

I agree that I think the cooler will be easier to use, but I can't visualize how one process converts to the other, or if there are other calculations that I need to make to take a recipe that calls for the standard PM method and convert it to using the cooler/mash tun?