Digital BW, The Print

I am considering purchasing either one of these two printers. 
Basically I want the same quality as i am getting with my 1290 with 
UT2 MIS inks but want to be able to produce prints 20" x 16" thus i 
need an upgrade. 

 The 4000 seems cheaper if you can find one by around £400 which i 
would prefer, but is the 4800 that much better?

Like i said i only need it for black and white and would convert it 
instantly to MIS UT2 inks if i choose either one.

Any advice would apprciated.

many thanks