Hello,
Migrating from Symantec Endpoint Protection v.11.0.5002 clients to Install Symantec Endpoint Protection v.12.1.RU1 could migrate flawlessly without any issues.
Yes, you migration would in the manner below:
SEPM 11.x --->> SEPM 12.1 RU1 ----->> SEPM 12.1 RU1 MP1
It is always recommended to perform a Disaster Recovery for SEPM 11.x before Migrating to SEP 12.1 as a Backup step.
Here are few steps to look at for Migration:
1) How to upgrade the Symantec Endpoint Protection Manager (SEPM) to Version 12.1 RU1
http://www.symantec.com/docs/TECH176260
2) a) Upgrading or migrating to Symantec Endpoint Protection 12.1.1000 (RU1)
http://www.symantec.com/business/support/index?page=content&id=TECH174545
b) Upgrading or migrating to Symantec Endpoint Protection 12.1.1101 (RU1 MP1)
http://www.symantec.com/business/support/index?page=content&id=TECH187753
3) Steps to prepare computers to install Symantec Endpoint Protection 12.1 client
http://www.symantec.com/docs/TECH163112
4) Activating your Symantec Endpoint Protection 12.1 product license
http://www.symantec.com/business/support/index?page=content&id=TECH162623
Also, check the Articles for the Migration on :
Quick Access to Symantec Knowledgebase Articles of Symantec Endpoint Protection 12.1
https://www-secure.symantec.com/connect/articles/quick-access-symantec-knowledgebase-articles-symantec-endpoint-protection-121
SEP 11.x to SEP 12.1 Upgrade process graphical overview
https://www-secure.symantec.com/connect/articles/sep-11x-sep-121-upgrade-process-graphical-overview
WhitePaper for Migration: https://www-secure.symantec.com/connect/downloads/migration-whitepaper-symantec-endpoint-protection-version-121
Secondly about GUP and Bandwidth, check these Articles:
Tips For Installing SEP In A Low Bandwidth Environment
'How to configure GUP bandwidth throttling in Symantec Endpoint Protection 11.0 MR4?'
Configuring the Group Update Provider (GUP) in Symantec Endpoint Protection 11.0 RU5 and later
Hope that helps!!