upgrade 3.7 to 6.1

Currently we have a site in Sitefinity 3.7. We are facing few performance issues in few areas. 

How much we can improve the performance by upgrading current site to latest Version? 
Like we have news which have more 30 lacks, will take lot of time to load in Admin site. I heard that in 3.7 adding a custom field will add a new row in a table rather in latest it adds as a column in a table. Will this improve the performance of loading the heavy articles?

Recently we conducted a Load Test on the website and concluded that every page is giving a call toCmsEntryPoint.aspx page which is taking moretime to load. Is there anything we can do to reduce this load time? Does customizing and adding custom controls effect this performance? 
How much will this be resolved by upgrading to latest version?

Can we upgrade our 3.7 site to latest version directly without any intermediate version? 
What will be the MIGRATION DIFFICULTY if we have any customization in our site?

My experience with migration is to not migrate users...it creates an annoying new membership provider so you then have to deal with 2...or try to remove default then every api call requires you to pass in the other provider...like certainly isn't a BIG PROBLEM, just annoying.

Migrating all other content for me went quite smooth though.

Steve

Hello,

I have provided a reply to your question in the other post you have created (link here).

Regards,
Ivaylo Angelov
Telerik

Hello,

I have provided a reply to your question in the other post you have created (link here).

Regards,
Stefani Tacheva
Telerik