Need Help to find an optimal confirguration for TCP/IP setting

[keliori]

Hello guys,

I'm confuse about several things in order to set up a proper TCP/IP settings

1st is MTU value
When I'm using SG TCP Optimizer software to test the largest MTU I could possibly use it says 1500.
But no matter what value I put into my MTU, when I do test with TCP/IP Analyzer the result for my MTU is always 1440 (MSS=1400). I personally think it's limited by my ISP. Am I correct here?
My question is what value should I put into my MTU? 1500 or 1440?

2nd is RWIN value
At this moment I'm using 1440 as my MTU value, and 64400 as RWIN value with Window Scaling Unchecked.
I checked modified all network adapter when I set it up. Then I do test again with TCP/IP Analyzer, something weird happens here.

I used to have many web browsers installed in my PC.
When I'm doing the test with IE, Firefox, Opera the result is MTU 1440, MSS 1400, RWIN 64400 (as expected I guess)
But when I'm doing the test with Chromium based web browsers like Google Chrome, Chromium, SRWare Iron, and Maxthon 3 I get this result: MTU 1440, MSS 1400, RWIN 65536. I have no idea where is RWIN value coming from?

Can anybody here help me answering my questions above? Some explanation "behind the scene" that cause this and that would be much appreciated.

PS: For your information I'm using a wireless mobile broadband ISP and USB modem connected directly to my PC (I don't use router).

[Rollingstone]

MTU Limitation : by ISP or Modem MTU & MSS (MSS = MTU -40) configuration & firmware

RWIN : Chrome based browser's TCP Window always show 65536 in XP !