Sir, Actually, when you set your MTU for 1500 / Default it will truncate the packet size automatically if you run into a router that uses a smaller packet size. There is really no performance benifit to adjusting it. I can only see your ping times getting worse as I think of it. I am not sure if you understand packet sizes, so here is a smal analogy:
Assume you want to send me a huge painting. Through the snail mail, using strandard business letter envelopes. You would have to cut up the painting, number it, address it, send it. The envelope is thepacket size. When it comes to me, open them, check the number (and ask for the missing ones if they are missing), then reasemble them to make the painting. Say it takes 10,000 envelopes to complete this.
Now assume you want to (for whatever reason) send the same painting in smaller envelopes (smaller packet sizes). You would have to send it in many more envelopes, like 20,000 or so. So, naturally it would take longer to process and complete this process. The only practical reason to do such a thing, is because your have a tiny mail box - this would be your ISP and how you actually see it. After that point, you do not care about packet sizes, for the internet will regulate those things at the ISP levels. I had to make adjustments one time on a clients computer, but is was foe her MAC OS X laptop and an ISP that had a smaller Packet size requirement.
When you game, there is alway this two way connection, however it will adjust itself, and you should concentrate on becoming a better pilot rather than tweeking the internet. To concude, I recommend to use the default that is set in your router.
