big tyres and transfer ratio ?

can any 1 put me right with this

iv a 95 300tdi

it has 35 /12.50 / 15 tyres
standard diffs the are 3.54 ?
standard transfer box that is 1,22 ? ?

iv been told to put 4,11 diffs in it to get my gearing back as i can use 5th at the mo

iv been under the truck today and found play in the transfer box front bearing so thinking about changing the transfer box that with sort the gearing as well

if im right and i have the 1,22 box i need to fit a 1,44 box ? just found a upgraded transfer box on ebay that has a 1.6 ratio , is that going to far ? im not interested in going that fast in it just dont want to be flat out a 50 mph

cheers

1.6 will be goin too far unless it is only used off road, put a 1.4 init

cheers
its mainly off road but i will tow with it , 1.4 it is then
any idear what top speed would be with the 1.6 ?
i will be keeping the standard 3.45 diffs